fix: Fix iOS build CI (`.xcframework` missing)

[mrousavy]

Summary

Fixes the build CI which previously failed silently.

See the last actions run, in the end of the logs it fails silently:

-- Up-to-date: /Users/runner/work/hermes/hermes/build_appletvsimulator/../destroot/include/jsi/decorator.h
-- Up-to-date: /Users/runner/work/hermes/hermes/build_appletvsimulator/../destroot/include/jsi/threadsafe.h
-- Up-to-date: /Users/runner/work/hermes/hermes/build_appletvsimulator/../destroot/include/jsi/jsilib.h
Creating universal framework for platforms: iphoneos iphonesimulator catalyst xros xrsimulator appletvos appletvsimulator
error: the path does not point to a valid framework: /Users/runner/work/hermes/hermes/destroot/Library/Frameworks/iphoneos/hermes.framework
rm: iphoneos: No such file or directory
rm: appletvos: No such file or directory
/Users/runner/work/hermes/hermes

This is fixed by upgrading macOS 14 to macOS 15, or more precise; upgrading Xcode 15.4 to Xcode 16 (which is always installed on a macos-15 runner, hence the removal of that unneeded extra action)

This is inspired by mrousavy/hermes-release-build, which I just created for this. It works on my CI with macos-15 and Xcode 16 now.

Test Plan

Run the CI and check logs