Require Click 7.0+

[jakirkham]

As Dask now includes this requirement and has a minimum of Click 7.0, go ahead and align on that version in Distributed.

xref: dask/dask#9595

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

[github-actions]

Unit Test Results

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

       15 files  ±0         15 suites  ±0   6h 29m 9s ⏱️ - 4m 17s
  3 165 tests ±0    3 079 ✔️  - 1    84 💤 ±0  2 ❌ +1 
23 416 runs  ±0  22 511 ✔️  - 1  901 💤 ±0  4 ❌ +1 

For more details on these failures, see this check.

Results for commit 33b64d9. ± Comparison against base commit 1db2595.

[jrbourbeau]

Thanks @jakirkham. Over in #4794 I also saw that we needed to bump our minimum version of click in order to get conda solve to work (similar to what we saw over in dask/dask). Bumping to 7.0 and matching dask/dask seems reasonable to me.

[jakirkham]

Interesting that's a little surprising. In any event, if this helps, great!