[FLINK-33378] Prepare actions for flink version 1.18

[eskabetxe]

Changes made:

• downgrade flink version on pom to match rule of minimum supported version
• added validation on PRs for 1.16 (this is already on weekly)
• bump version from 1.18-SNAPSHOT to 1.18.0 on all gitactions
• bump the version of some test dependencies as Junit5, assertj, testcontainers and mockito

Note:

• version 1.19-SNAPSHOT is not added to CI because of this

[maver1ck]

@MartijnVisser any chance to merge this ?

[eskabetxe]

I have a problem now..
This was merged: https://issues.apache.org/jira/browse/FLINK-29541

Basically this class TableTestBase have been migrated to junit5, and this makes JdbcTablePlanTest fail on 1.19-SNAPSHOT

@snuyanzin any guidance? can I remove 1.19-SNAPSHOT to allow this to be merged?

[snuyanzin]

can I remove 1.19-SNAPSHOT to allow this to be merged?

yes, I think we could it split it into some subtasks

[eskabetxe]

@snuyanzin removed the 1.19-SNAPSHOT from PRs and Weekly.. all green

[snuyanzin]

great, thanks
can you also change PR's description to match changes within this PR?

[eskabetxe]

can you also change PR's description to match changes within this PR?

done

[snuyanzin]

@MartijnVisser are you ok or you'd like to have anything else improved?
(asking since you are marked as one who requested changes)

[snuyanzin]

ok, let's merge it