Warning for CLIP Score on long captions

[SkafteNicki]

What does this PR do?

Fixes #2000

Before submitting

• Was this discussed/agreed via a Github issue? (no need for typos and docs improvements)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure to update the docs?
• Did you write any new necessary tests?

PR review

Anyone in the community is free to review the PR once the tests have passed.
If we didn't discuss your PR in Github issues there's a high chance it will not be merged.

Did you have fun?

Make sure you had fun coding 🙃

---

📚 Documentation preview 📚: https://torchmetrics--2001.org.readthedocs.build/en/2001/

[codecov]

Codecov Report

Merging #2001 (6832af1) into master (3b3b997) will decrease coverage by 52%.
The diff coverage is 17%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #2001     +/-   ##
========================================
- Coverage      87%     34%    -52%     
========================================
  Files         268     268             
  Lines       15427   15433      +6     
========================================
- Hits        13360    5286   -8074     
- Misses       2067   10147   +8080