9169 fix duplicate keys in Java properties files

[poikilotherm]

What this PR does / why we need it: Fix duplicated keys in all *.properties. Add Github Action to check for no re-introduction of dups.

Which issue(s) this PR closes:

Closes #9169

Special notes for your reviewer: Feel free to push to this branch for fixing all of the dups in the same go. I don't mind!

Suggestions on how to test this: Look at the PRs Action log

Does this PR introduce a user interface change? If mockups are available, please link/include them here: Nope

Is there a release notes update needed for this change?: Nope

Additional documentation: None

[poikilotherm]

This PR now contains a test commit (33731ad), which needs to be reverted before merging.

Here is the output of the verification job:

Here is the output of the duplication check job:

That one also leaves notes in the changes tab:

[poikilotherm]

As you can see, it already detected a missing property in CodeMeta and a typo - fixed with 1aeb665.

[pdurbin]

We're having a wee problem with this script. See the Slack thread and this issue:

• #10826