Upgrade to macos-13 and 15, use DRY for Mac jobs

[sirknightj]

Issue #, if available:

What was changed?

• Actually use the GCC compiler for Mac-GCC jobs.
• Factor out the Mac jobs to use the matrix strategy for more maintainable code

Why was it changed?

• MacOS-12 runner is deprecated and blocking the other PR from getting merged: Samples: Fit the RTP transceiver rolling buffers to fit the set of sample frames #2089

How was it changed?

• CI file was modified to include the changes above.
• Note that the GCC+Mac+Unit Tests combination was skipped. The GCC job previously used Clang 14. Now that it actually correctly uses GCC-14, AWS CRT CPP does not support this combination of GCC on Apple Silicon Macs: Build Issue with M1 MacOS and GCC aws-crt-cpp#605. Note that a different compile error for AWS SDK CRT occurs for GCC on the Intel Macs too:

/Applications/Xcode_15.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/usr/include/dispatch/queue.h:103:1: error: unknown type name 'dispatch_queue_t'; did you mean 'dispatch_time_t'?
  103 | DISPATCH_DECL_SUBCLASS(dispatch_queue_global, dispatch_queue);
      | ^~~~~~~~~~~~~~~~~~~~~~

What testing was done for the changes?

• Having GitHub actions run the updated CI.

By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice.

[sirknightj]

Warning: Formula gst-plugins-base was renamed to gstreamer.
Warning: Formula gst-plugins-good was renamed to gstreamer.
Warning: Formula gst-plugins-bad was renamed to gstreamer.
Warning: Formula gst-plugins-ugly was renamed to gstreamer.
Warning: Formula gst-libav was renamed to gstreamer.

[niyatim23]

Nice!