Add test when not repartitioning for p2p in set_index

[phofl]

xref #8015

• Tests added / passed
• Passes pre-commit run --all-files

cc @hendrikmakait

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

       13 files   -        1         13 suites   - 1   6h 15m 18s ⏱️ - 41m 28s
  3 719 tests +       1    3 609 ✔️ +       3     108 💤 ±  0  2 ❌  - 2 
23 594 runs   - 1 312  22 449 ✔️  - 1 275  1 143 💤  - 35  2 ❌  - 2 

For more details on these failures, see this check.

Results for commit 625b979. ± Comparison against base commit d9a3457.

[jrbourbeau]

Thanks for adding a test @phofl

Are we sure this is testing what we want? This test passes when using the main branch of dask without dask/dask#10421

[phofl]

We are just checking that the change does not break anything, it is supposed to pass on both versions

[jrbourbeau]

Ah, I thought we were wanting to check that the extra repartition doesn't happen with p2p

[phofl]

No just that behavior won’t change (that was my intent at least)