[v3-3-test] Fix the RAT licence check excludes and move it to Apache RAT 0.18 (#73064)

[github-actions]

• Make the RAT licence check ignore IntelliJ module files again

The exclude entry for these was written as a regex, .*.iml, but RAT matches
exclude patterns as globs against the full path. That form needs two dots to
match, so airflow-core.iml and its 76 siblings never matched it and the check
reported 77 unapproved licences for anyone who had opened the repo in
IntelliJ. The files are gitignored and so never reach a source tarball, which
is why the release-time check stayed green and the breakage only ever showed
up locally.

Use the same **/ form the rest of the file already uses for patterns that
have to match at any depth.

Generated-by: Claude Opus 5
Claude-Session: https://claude.ai/code/session_012zrnHJHPchB83FtwrYRf5q

• Rebuild the Apache RAT image on RAT 0.18

The image reference has stayed on RAT 0.17 since 0.18 was adopted everywhere
else, because the 0.18 image was never built: the release docs, the release
validator and this script were all moved to 0.18, but no 0.18 tag was ever
pushed, so the prek hook kept pulling the 0.17 image. Dating the image afresh
gives the 0.18 build a tag of its own rather than overwriting a published one.

Generated-by: Claude Opus 5
Claude-Session: https://claude.ai/code/session_012zrnHJHPchB83FtwrYRf5q

• Run the licence check on Apache RAT 0.18

This was the one reference left behind when RAT 0.18 was adopted, so the
check has been running 0.17 while the release docs and the release validator
told everyone else to use 0.18. Point it at the freshly built 0.18 image,
pinned by index digest as before so both architectures resolve.

Generated-by: Claude Opus 5
Claude-Session: https://claude.ai/code/session_012zrnHJHPchB83FtwrYRf5q

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(cherry picked from commit ba7a45e)

Co-authored-by: Jarek Potiuk jarek@potiuk.com
Co-authored-by: Rahul Vats 43964496+vatsrahul1001@users.noreply.github.com

[potiuk]

already merged.