CI: lower audio test size

[SkafteNicki]

What does this PR do?

SDR / SNR test times are often among the highest and sometimes (too often) above the timeout threshold.
Try with smaller input to lower computations.

Example:
https://dev.azure.com/Lightning-AI/Metrics/_build/results?buildId=150556&view=logs&j=b817243f-a6e0-5fef-3435-47908ec3a6b7&t=172d1999-bd63-576d-9fa3-c0fe8e5a5e24

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 🙃

[codecov]

Codecov Report

Merging #1718 (0bedfdc) into master (f17afcb) will decrease coverage by 50%.
The diff coverage is 20%.

Additional details and impacted files

@@           Coverage Diff            @@
##           master   #1718     +/-   ##
========================================
- Coverage      88%     38%    -50%     
========================================
  Files         238     238             
  Lines       13331   13360     +29     
========================================
- Hits        11722    5052   -6670     
- Misses       1609    8308   +6699