fix: codecov does not allow '/' in the name of coverage flags

[eseidel]

So fixed by using a stack overflow answer of how to split a
path in GitHub actions. Now we only pass the package name
not the entire path.

Could consider moving this out of the action, and have the package
name be an input?

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -2.17% ⚠️

Comparison is base (a916d7d) 100.00% compared to head (fb6eb85) 97.83%.
Report is 4 commits behind head on main.

❗ Current head fb6eb85 differs from pull request most recent head fdf5211. Consider uploading reports for the commit fdf5211 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##              main    #1168      +/-   ##
===========================================
- Coverage   100.00%   97.83%   -2.17%     
===========================================
  Files           81      179      +98     
  Lines         3181     4518    +1337     
===========================================
+ Hits          3181     4420    +1239     
- Misses           0       98      +98     

Flag	Coverage Δ
artifact_proxy	100.00% <ø> (?)
cutler	14.03% <ø> (?)
discord_gcp_alerts	100.00% <ø> (?)
jwt	100.00% <ø> (?)
redis_client	100.00% <ø> (?)
scoped	100.00% <ø> (?)
shorebird_cli	100.00% <ø> (?)
shorebird_code_push_client	100.00% <ø> (?)
shorebird_code_push_protocol	100.00% <ø> (?)

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see 98 files with indirect coverage changes

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[eseidel]

Landing as this is strictly better than what we have now on main. I will separately look into why cutler isn't being held to only 10%.