W-23212499: Fix iOS 18 / Xcode 16 CI jobs broken by macos-latest → macOS 26 migration

[wmathurin]

Summary

• GitHub migrated macos-latest to macOS 26 on June 15, 2026, which no longer ships Xcode 16 or iOS 18 simulators.
• Jobs using ios: ^18 / xcode: ^16 were failing because they landed on macOS 26 via macos-latest.
• Added macos: macos-15 to the ^18/^16 matrix include entry in all three caller workflows, and threaded macos: ${{ matrix.macos }} through to the reusable workflow with: blocks.
• The ^26/^26 entries are left unchanged — they should continue using macos-latest (now macOS 26).
• The reusable workflow files are not modified; they already accept macos as an optional input with default: macos-latest.

Files changed

• .github/workflows/pr.yaml — jobs: ios-pr, native-samples-pr, ui-tests-pr
• .github/workflows/nightly.yaml — jobs: ios-nightly, native-samples-nightly
• .github/workflows/ui-test-nightly.yaml — job: ios-ui-test-nightly

Test plan

• Verify PR CI (ios-pr, native-samples-pr, ui-tests-pr) picks up macos-15 runner for the ^18/^16 matrix leg
• Verify ^26/^26 matrix leg still runs on macos-latest
• Confirm nightly run succeeds after merge

[github-actions]

	Tests	Passed	Skipped	Failed ❌️
AuthFlowTester UI Test Results all	1 ran			1 ❌

Test	Result
AuthFlowTester UI Test Results all
AuthFlowTesterUITests.xctest
LegacyLoginTests.testCAOpaque_DefaultScopes_WebServerFlow()	❌ failure

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.42%. Comparing base (10c1396) to head (afa4abd).
⚠️ Report is 1 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #4090      +/-   ##
==========================================
+ Coverage   66.71%   68.42%   +1.70%     
==========================================
  Files         246      246              
  Lines       21541    21541              
==========================================
+ Hits        14372    14740     +368     
+ Misses       7169     6801     -368     

Components	Coverage Δ
Analytics	70.78% <ø> (ø)
Common	70.79% <ø> (ø)
Core	62.04% <ø> (+2.61%)	⬆️
SmartStore	73.44% <ø> (-0.16%)	⬇️
MobileSync	88.79% <ø> (+0.23%)	⬆️
see 22 files with indirect coverage changes

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[github-actions]

	Tests	Passed ✅	Skipped	Failed
SalesforceSDKCore iOS ^26 Test Results	675 ran	675 ✅

Test	Result
No test annotations available

[github-actions]

	Tests	Passed ☑️	Skipped	Failed ❌️
SalesforceSDKCore iOS ^18 Test Results	675 ran	674 ✅		1 ❌

Test	Result
SalesforceSDKCore iOS ^18 Test Results
SalesforceRestAPITests.testUpdateWithIfUnmodifiedSince	❌ failure

[sfdctaka]

LGTM!