Update evergreen to use xcode 15.3

[jbreams]

What, How & Why?

At some point the build hosts were updated to use xcode 15.3 instead of xcode 15.2 and so we're failing to compile on new build hosts. This just bumps the version in tests.

☑️ ToDos

• 📝 Changelog update
• 🚦 Tests (or not relevant)
• C-API, if public C++ API changed
• bindgen/spec.yml, if public C++ API changed

[coveralls-official]

Pull Request Test Coverage Report for Build jonathan.reams_3461

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 41 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.3%) to 91.132%

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Files with Coverage Reduction	New Missed Lines	%
src/realm/sync/instruction_applier.cpp	5	68.33%
src/realm/sync/noinst/server/server_history.cpp	6	62.59%
test/fuzz_group.cpp	30	52.47%

Totals
Change from base Build 2624:	0.3%
Covered Lines:	217259
Relevant Lines:	238400

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💛 - Coveralls