How to change Xcode/CLT version in CI/Github Actions

[Dave Allured - NOAA Affiliate]

The default CLT version for the Ventura/OS13 CI was recently updated to CLT
15.0.  This brings all the love and joy of Xcode 15.0 anomalies to
CI/Github Actions.  This is obstructing normal portfile development and
testing for the otherwise standard Macports CI workflow.  I have recently
experienced on the OS13 CI:

* Xcode/CLT mismatch:
2023-11-20T23:30:48.9369220Z DEBUG: Xcode 14.3.1, CLT 15.0.0.0.1.1694021235

* 15.0 linker problem:
2023-11-20T23:43:13.2834120Z ld: duplicate LC_RPATH '/opt/local/lib/libgcc'
in '/opt/local/lib/libnetcdff.7.dylib'

The linker problem is addressed in several tickets, mainly trac #68329, so
no sense to rehash those details here.  Yes it is the same problem, no
longer confined to just Sonoma.

Is there an easy way to select a specific Xcode or CLT version for CI
workflows?  Developers could insert such temporary control into individual
PR's, to be excluded upon merging.   Alternatively, Macports could insert
this into macports-ports/master for community benefit, while we ride out
the wait for Apple fixes or other solutions.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.macports.org/pipermail/macports-dev/attachments/20231120/bc968e6e/attachment.htm>