Upgrade nightly macOS version to macos 15

[shivammathur]

This PR upgrades macOS version in the nightly workflow as macos-13 has been deprecated and will be discontinued soon. The next x86_64 macOS version they have added in macOS 15.
(actions/runner-images#13046)
So, we can upgrade to.

• macOS 15 (macos-15-intel) for all x86_64 runs.
• macOS 15 for 8.5 and master. we can keep macOS 14 for 8.1 to 8.4 for arm64.

Issues Identified on macOS 15.

• JIT TLS changes in macos 15 causes segfaults. (Fixed in Fix JIT TLS on MacOS 15 #20121)
• Test ext/ctype/tests/lc_ctype_inheritance.phpt fails on macOS 15 as it inherits LC_CTYPE into the thread locale. We can skip the test on macos 15 as the issue is a due to a change by Apple as discussed in str_word_count behaves differently on macos 14 vs 15+ #19828.
• 8.1 does not build on macos 15 with this error (no_caller_saved_registers function calls memcmp (Zend/zend_string.c:389). Logs . We can backport 6339938 in PHP-8.1 (patch), but I'm not sure as the branch is now for security-fixes only.

[iluuu1994]

Thank you for this PR. It does look correct to me.

We can backport 6339938 in PHP-8.1 (patch), but I'm not sure as the branch is now for security-fixes only.

If this is the only necessary change it seems ok, but RMs should confirm.

[iluuu1994]

Thanks @shivammathur for handling this!