launchpad build of microovn results in version suffixed by -dirty

[Frode Nordahl]

The MicroOVN version string code [0] passes the `--dirty` option to ensure any manually built snap with local changes can be identified.

Surprisingly the version string produced during a Launchpad build [1] currently provides a version string indicating a dirty build.

We ought to figure out why that is.

0: https://github.com/canonical/microovn/blob/994eb5e4490274e1a4b5c03725d8ba1905f92c90/snap/snapcraft.yaml#L282
1: https://launchpad.net/~ubuntu-ovn-eng/microovn/+snap/microovn-main/+build/2555943