[ci] Roll pinned nightly toolchain

[google-pr-creation-bot]

Automated changes by create-pull-request GitHub action

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.42%. Comparing base (6450181) to head (6c86dc7).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2484   +/-   ##
=======================================
  Coverage   90.42%   90.42%           
=======================================
  Files          19       19           
  Lines        7523     7523           
=======================================
  Hits         6803     6803           
  Misses        720      720           

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