commit access policy: clarify that only current module owners/peers can vouch

[globau]

Updates the Commit Access Policy to make it clear that a vouch is required from a current owner or peer; vouches from former owners/peers are insufficient.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 76.57%. Comparing base (bce44fb) to head (a73c54c). Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #14288   +/-   ##
=======================================
  Coverage   76.57%   76.57%           
=======================================
  Files         144      144           
  Lines        7800     7800           
=======================================
  Hits         5973     5973           
  Misses       1827     1827           

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