please fix build tests

[Mark Esler]

hi o/

./debian/rules states:
```
# The ignored pkgs are aligned with upstream ./test file,
# see variables IGNORE_PKGS and INTEGRATION_PKGS in ./test
export TEST_EXCLUDES := cmd/ etcdserverpb rafttest gopath.proto v3lockpb v3electionpb \
                        integration e2e contrib functional
```

./test contains:
```
IGNORE_PKGS="(vendor/|etcdserverpb|rafttest|gopath.proto|v3lockpb|v3electionpb)"
INTEGRATION_PKGS="(integration|tests/e2e|contrib|functional)"
```
INTEGRATION_PKGS _are_ later used in ./test and IGNORE_PKGS are excluded from testing _by upstream_.

TEST_EXCLUDE does not align with the logic of upstream ./test.

INTEGRATION_PKGS should be tested in the Debian/Ubuntu packages. Testing etcd's e2e is critical for security of Kubernetes.

On Ubuntu Mantic, the package builds well with `integration` and `contrib` tests (i.e., when they are removed from TEST_EXCLUDES). `e2e` needs to be patched to put package binaries in the PATH of tests--other issues may also exist. `functional` tests also ftbfs.

[Shengjing Zhu (zhsj)]

integration tests are run in autopkgtest https://salsa.debian.org/go-team/packages/etcd/-/blob/debian/3.4.23-4/debian/tests/integration

[Shengjing Zhu (zhsj)]

functional tests are also in autopkgtest

[Shengjing Zhu (zhsj)]

But the tests are failing on Ubuntu... https://autopkgtest.ubuntu.com/packages/e/etcd/mantic/amd64

[Mark Esler (eslerm)]

Thank you Shengjing!

Security has autopkgtests for ESM, so that might work for patching. Build tests would be ideal.

From the autopkgtests, there's a consistent failure which might be an upstream issue:
```
go.etcd.io/etcd/clientv3/balancer/picker
# go.etcd.io/etcd/clientv3/balancer/picker
src/go.etcd.io/etcd/clientv3/balancer/picker/err.go:23:9: cannot use &errPicker{…} (value of type *errPicker) as type Picker in return statement:
        *errPicker does not implement Picker (wrong type for Pick method)
                have Pick(balancer.PickInfo) (balancer.PickResult, error)
                want Pick(ctx context.Context, info balancer.PickInfo) (conn balancer.SubConn, done func(balancer.DoneInfo), err error)
src/go.etcd.io/etcd/clientv3/balancer/picker/roundrobin_balanced.go:32:9: cannot use &rrBalanced{…} (value of type *rrBalanced) as type Picker in return statement:
        *rrBalanced does not implement Picker (wrong type for Pick method)
                have Pick(opts balancer.PickInfo) (balancer.PickResult, error)
                want Pick(ctx context.Context, info balancer.PickInfo) (conn balancer.SubConn, done func(balancer.DoneInfo), err error)
```
the above stanza is not in every log, but the below is:
```
=== RUN TestRoundRobinBalancedResolvableNoFailover/rrBalanced_1_unix_sockets
{"level":"debug","msg":"registered balancer","policy":"picker-roundrobin-balanced","name":"175BC073483F97E22"}
{"level":"info","msg":"built balancer","balancer-id":"cscz1v8kv8pc","policy":"picker-roundrobin-balanced","resolver-target":"endpoint://nofailover/*"}
{"level":"info","msg":"resolved","picker":"picker-error","balancer-id":"cscz1v8kv8pc","addresses":["unix:///tmp/etcd-unix-so-3384251395"]}
{"level":"info","msg":"created subconn","address":"unix:///tmp/etcd-unix-so-3384251395"}
{"level":"info","msg":"state changed","picker":"picker-error","balancer-id":"cscz1v8kv8pc","connected":false,"subconn":"0xc00017b0c0","subconn-size":1,"address":"unix:///tmp/etcd-unix-so-3384251395","old-state":"IDLE","new-state":"CONNECTING"}
{"level":"warn","msg":"connectivity recorder received unknown state","connectivity-state":"IDLE"}
{"level":"info","msg":"state changed","picker":"picker-error","balancer-id":"cscz1v8kv8pc","connected":false,"subconn":"0xc00017b0c0","subconn-size":1,"address":"unix:///tmp/etcd-unix-so-3384251395","old-state":"CONNECTING","new-state":"TRANSIENT_FAILURE"}
{"level":"info","msg":"updated picker to transient error picker","picker":"picker-error","balancer-id":"cscz1v8kv8pc","policy":"picker-roundrobin-balanced"}
    balancer_test.go:96: Unexpected failure rpc error: code = Unavailable desc = all SubConns are in TransientFailure
[...]
--- FAIL: TestRoundRobinBalancedResolvableNoFailover (0.02s)
    --- PASS: TestRoundRobinBalancedResolvableNoFailover/rrBalanced_1 (0.00s)
    --- FAIL: TestRoundRobinBalancedResolvableNoFailover/rrBalanced_1_unix_sockets (0.01s)
```

These are flakey tests which fail due to timeout and can likely be ignored:
```
--- FAIL: TestBalancerUnderNetworkPartitionWatchFollower (4.17s)
--- FAIL: TestBalancerUnderNetworkPartitionDelete (8.16s)
--- FAIL: TestCtlV3AuthCertCNWithWithConcurrentOperation (60.66s)
--- ...