Don't use CARGO_REGISTRIES_* configuration in hash keys

[kornelski]

Private registry configuration in Cargo can be specified using CARGO_REGISTRIES_$name_* env vars. That it includes CARGO_REGISTRIES_$name_TOKEN, which is an auth secret. The tokens have high entropy and change often, so inclusion of such env vars in the hash key completely ruins caching in sccache.

I don't think any of the CARGO_REGISTRIES_ env vars need to be tracked, because Cargo identifies dependencies by their package IDs, which already includes a normalized registry URL. Only the resolved package ID affects the result, not the mechanics of how Cargo discovered it.

[Xuanwo]

Makes sense. Thank you @kornelski for this!

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (0cc0c62) to head (8642030).
Report is 128 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #2308       +/-   ##
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- Coverage   30.91%       0   -30.92%     
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  Files          53       0       -53     
  Lines       20112       0    -20112     
  Branches     9755       0     -9755     
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- Hits         6217       0     -6217     
+ Misses       7922       0     -7922     
+ Partials     5973       0     -5973     

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