chore(build): update setup-ruby github action for macos-15 runners

[thisisabhash]

Issue #

Github actions are failing for setup-ruby after updating runners to macos-latest which correspond to macos-15 now.
https://github.com/aws-amplify/amplify-swift/actions/runs/17246673926

Error message:

The current runner (macos--arm64) was detected as self-hosted because the platform does not match a GitHub-hosted runner image (or that image is deprecated and no longer supported).
In such a case, you should install Ruby in the $RUNNER_TOOL_CACHE yourself, for example using https://github.com/rbenv/ruby-build
You can take inspiration from this workflow for more details: https://github.com/ruby/ruby-builder/blob/master/.github/workflows/build.yml
$ ruby-build 3.2.1 /Users/runner/hostedtoolcache/Ruby/3.2.1/arm64
Once that completes successfully, mark it as complete with:
$ touch /Users/runner/hostedtoolcache/Ruby/3.2.1/arm64.complete
It is your responsibility to ensure installing Ruby like that is not done in parallel.

Description

Updating setup-ruby to v1.256.0.

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]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.63%. Comparing base (1d60201) to head (1ca011c).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4045      +/-   ##
==========================================
- Coverage   67.80%   67.63%   -0.17%     
==========================================
  Files        1129     1117      -12     
  Lines       52482    52136     -346     
==========================================
- Hits        35583    35260     -323     
+ Misses      16899    16876      -23     

Flag	Coverage Δ
API_plugin_unit_test	70.33% <ø> (ø)
AWSPluginsCore	69.25% <ø> (ø)
Amplify	47.93% <ø> (ø)
Analytics_plugin_unit_test	85.20% <ø> (ø)
Auth_plugin_unit_test	73.56% <ø> (-0.09%)	⬇️
DataStore_plugin_unit_test	83.32% <ø> (-0.04%)	⬇️
Geo_plugin_unit_test	74.86% <ø> (ø)
Logging_plugin_unit_test	65.27% <ø> (ø)
Predictions_plugin_unit_test	34.77% <ø> (ø)
PushNotifications_plugin_unit_test	?
Storage_plugin_unit_test	79.39% <ø> (ø)
unit_tests	67.63% <ø> (-0.17%)	⬇️

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