ci: Update Xcode to 15.4

[cbaker6]

New Pull Request Checklist

• I am not disclosing a vulnerability.
• I am creating this PR in reference to an issue.

Issue Description

Update to Xcode 15.4 and the macOS 14 image which uses Apple Silicon by default.

Approach

• Install SwiftLint onto image as macOS 14 image doesn't contain this (unlike previous images)
• Remove enabling multiple cores as this setting was for Intel based images
• Set the CI iOS and tvOS to 17.5 and visionOS to 1.2
• Remove visionOS build/test for now

TODOs before merging

• Verify visionOS builds and passes

[codecov]

Codecov Report

Attention: Patch coverage is 86.36364% with 6 lines in your changes missing coverage. Please review.

Project coverage is 91.26%. Comparing base (077d457) to head (2992309).

Files	Patch %	Lines
Sources/ParseSwift/Extensions/URLSession.swift	0.00%	2 Missing ⚠️
...rces/ParseSwift/Protocols/ParseOperationable.swift	66.66%	1 Missing ⚠️
Sources/ParseSwift/Protocols/ParseTypeable.swift	66.66%	1 Missing ⚠️
Sources/ParseSwift/Types/ParseFieldOptions.swift	66.66%	1 Missing ⚠️
Sources/ParseSwift/Types/ParseOperation.swift	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   91.21%   91.26%   +0.05%     
==========================================
  Files         178      178              
  Lines       12087    12079       -8     
==========================================
- Hits        11025    11024       -1     
+ Misses       1062     1055       -7     

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[cbaker6]

visionOS build currently failing due to actions/runner-images#9511