chore: Caching the build folder for unit test schemes

[ruisebas]

Description

In order to speed up running unit tests, this PR makes the following changes:

• We will now cache the Build folder used when running tests in main, per scheme per platform.
• When we run a test, if there is no build cache for the specific SHA (existing behaviour) we will now retrieve the build cache from main, so that xcodebuild would theoretically only need to build incrementally what has changed.
• GitHub Actions does not have direct support to overwrite/update caches, so we need to execute gh cache delete first in order to save it. We do this for every successfull test run, only in main.
  • Because of this, all the workflows that run tests now need to specify the actions: write permission for the GitHub token.
• I added a restore-key for the SHA caches so that we can retrieve old ones from previous commits. This was done mostly so we can now delete them when the test succeeds, so we don't end up with many orphaned caches if the tests are not re-run.

General Checklist

• Added new tests to cover change, if needed
• Build succeeds with all target using Swift Package Manager
• All unit tests pass
• All integration tests pass
• Security oriented best practices and standards are followed (e.g. using input sanitization, principle of least privilege, etc)
• Documentation update for the change if required
• PR title conforms to conventional commit style
• New or updated tests include Given When Then inline code documentation and are named accordingly testThing_condition_expectation()
• If breaking change, documentation/changelog update with migration instructions

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Merging #3200 (de8d064) into main (ac1a266) will decrease coverage by 0.06%.
Report is 3 commits behind head on main.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##             main    #3200      +/-   ##
==========================================
- Coverage   64.77%   64.71%   -0.06%     
==========================================
  Files        1090     1090              
  Lines       36999    36999              
==========================================
- Hits        23966    23944      -22     
- Misses      13033    13055      +22     

Flag	Coverage Δ
API_plugin_unit_test	66.52% <ø> (ø)
AWSPluginsCore	69.55% <ø> (ø)
Amplify	47.84% <ø> (-0.02%)	⬇️
Analytics_plugin_unit_test	86.39% <ø> (ø)
Auth_plugin_unit_test	75.11% <ø> (-0.15%)	⬇️
CoreMLPredictions_plugin_unit_test	59.44% <ø> (ø)
DataStore_plugin_unit_test	81.06% <ø> (-0.08%)	⬇️
Geo_plugin_unit_test	54.06% <ø> (ø)
Logging_plugin_unit_test	62.61% <ø> (ø)
Predictions_plugin_unit_test	35.17% <ø> (ø)
PushNotifications_plugin_unit_test	69.43% <ø> (ø)
Storage_plugin_unit_test	54.10% <ø> (ø)
unit_tests	64.71% <ø> (-0.06%)	⬇️

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see 11 files with indirect coverage changes

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