Log key collision count in `update_graph` log event

[hendrikmakait]

Blocked by #8691

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

[github-actions[bot]]

Unit Test Results

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

    29 files  ±    0      29 suites  ±0   11h 3m 38s :stopwatch: + 1h 13m 56s  4 060 tests  -     5   3 958 :white_check_mark: +    9     97 :zzz:  -   9  5 :x:  - 1  55 925 runs  +7 595  53 756 :white_check_mark: +7 366  2 163 :zzz: +249  6 :x:  - 3 

For more details on these failures, see this check.

Results for commit 786eefbf. ± Comparison against base commit af237f0d.

This pull request removes 13 and adds 8 tests. Note that renamed tests count towards both.

``` distributed.protocol.tests.test_arrow distributed.protocol.tests.test_collection distributed.protocol.tests.test_highlevelgraph distributed.protocol.tests.test_numpy distributed.protocol.tests.test_pandas distributed.shuffle.tests.test_graph distributed.shuffle.tests.test_merge distributed.shuffle.tests.test_merge_column_and_index distributed.shuffle.tests.test_metrics distributed.shuffle.tests.test_rechunk … ``` ``` distributed.diagnostics.tests.test_memray ‑ test_basic_integration_scheduler distributed.diagnostics.tests.test_memray ‑ test_basic_integration_scheduler_report_args[False] distributed.diagnostics.tests.test_memray ‑ test_basic_integration_scheduler_report_args[report_args0] distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers[1] distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers[False] distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers[True] distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers_report_args[False] distributed.diagnostics.tests.test_memray ‑ test_basic_integration_workers_report_args[report_args0] ```

:recycle: This comment has been updated with latest results.