I have tested the package and it seems to work as expected, steps taken:

First, some machine info:
```
root@ubuntu-test:~# lsb_release -a
No LSB modules are available.
Distributor ID:	Ubuntu
Description:	Ubuntu 22.04.2 LTS
Release:	22.04
Codename:	jammy

root@ubuntu-test:~# uname -a
Linux ubuntu-test 5.15.0-58-generic #64-Ubuntu SMP Thu Jan 5 11:43:13 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
```

Then we install the currently available version and verify it is broken:
```
root@ubuntu-test:~# apt install hiera-eyaml

root@ubuntu-test:~# dpkg -l hiera-eyaml
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version      Architecture Description
+++-==============-============-============-====================================
ii  hiera-eyaml    3.2.2-2      all          OpenSSL Encryption backend for Hiera

root@ubuntu-test:~# eyaml
/usr/share/rubygems-integration/all/gems/hiera-eyaml-3.2.2/lib/hiera/backend/eyaml/plugins.rb:37:in `block (2 levels) in find': undefined method `dependencies' for #<Gem::StubSpecification:0x000055a0108727f0 @extension_dir=nil, @full_gem_path=nil, @gem_dir=nil, @ignored=nil, @loaded_from="/usr/lib/ruby/gems/3.0.0/specifications/default/abbrev-0.1.0.gemspec", @data=#<Gem::StubSpecification::StubLine:0x000055a010871850 @name="abbrev", @version=#<Gem::Version "0.1.0">, @platform="ruby", @extensions=[], @full_name="abbrev-0.1.0", @require_paths=["lib"]>, @name=nil, @spec=nil, @base_dir="/var/lib/gems/3.0.0", @gems_dir="/var/lib/gems/3.0.0/gems", @default_gem=true> (NoMethodError)
	from /usr/share/rubygems-integration/all/gems/hiera-eyaml-3.2.2/lib/hiera/backend/eyaml/plugins.rb:34:in `each'
	from /usr/share/rubygems-integration/all/gems/hiera-eyaml-3.2.2/lib/hiera/backend/eyaml/plugins.rb:34:in `block in find'
	from /usr/share/rubygems-integration/all/gems/hiera-eyaml-3.2.2/lib/hiera/backend/eyaml/plugins.rb:31:in `each'
	from /usr/share/rubygems-integration/all/gems/hiera-eyaml-3.2.2/lib/hiera/backend/eyaml/plugins.rb:31:in `find'
	from /usr/share/rubygems-integration/all/gems/hiera-eyaml-3.2.2/bin/eyaml:10:in `<top (required)>'
	from /usr/bin/eyaml:25:in `load'
	from /usr/bin/eyaml:25:in `<main>'
```

Then we enable -proposed as detailed in https://wiki.ubuntu.com/Testing/EnableProposed:
```
root@ubuntu-test:~# cat <<EOF >/etc/apt/sources.list.d/ubuntu-$(lsb_release -cs)-proposed.list
# Enable Ubuntu proposed archive
deb http://archive.ubuntu.com/ubuntu/ $(lsb_release -cs)-proposed restricted main multiverse universe
EOF

root@ubuntu-test:~# cat <<EOF >/etc/apt/preferences.d/proposed-updates
# Configure apt to allow selective installs of packages from proposed
Package: *
Pin: release a=$(lsb_release -cs)-proposed
Pin-Priority: 400
EOF
```

Update apt and install the fixed package:
```
root@ubuntu-test:~# apt update

root@ubuntu-test:~# apt install -t jammy-proposed hiera-eyaml

root@ubuntu-test:~# dpkg -l hiera-eyaml
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name           Version          Architecture Description
+++-==============-================-============-====================================
ii  hiera-eyaml    3.2.2-2ubuntu0.1 all          OpenSSL Encryption backend for Hiera
```

Test the fixed tool:
```
root@ubuntu-test:~# eyaml
Unknown subcommand

Usage: eyaml <subcommand>

Please use one of the following subcommands or help for more help:
  createkeys, decrypt, edit, encrypt, recrypt, version


root@ubuntu-test:~# eyaml createkeys
[hiera-eyaml-core] Created key directory: ./keys
[hiera-eyaml-core] Keys created OK


root@ubuntu-test:~# eyaml edit foo.eyaml
[hiera-eyaml-core] foo.eyaml doesn't exist, editing new file
[... edit file as in initial report and save ...]

root@ubuntu-test:~# cat foo.eyaml
---
foo: ENC[PKCS7,MIIBeQYJKoZIhvcNAQcDoIIBajCCAWYCAQAxggE...]


root@ubuntu-test:~# eyaml edit foo.eyaml
[... content shows up unencrypted ...]
```