GHA: Use the shared workflow from Boost.CI for tests

[Flamefire]

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[mborland]

This is a very much appreciated improvement, but the workflow ran with 0 jobs?

[Flamefire]

I see, shouldn't have removed the customizations entirely

[Flamefire]

@mborland Seems Boost.Test doesn't work on Cygwin:

2026-06-25T11:50:22.2152487Z ./boost/test/impl/debug.ipp: In function 'const char* boost::debug::{anonymous}::prepare_gdb_cmnd_file(const boost::debug::dbg_startup_info&)':
2026-06-25T11:50:22.2224879Z ./boost/test/impl/debug.ipp:437:25: error: '::mkstemp' has not been declared; did you mean 'mkdtemp'?
2026-06-25T11:50:22.2264462Z   437 |     fd_holder cmd_fd( ::mkstemp( cmd_file_name ) );
2026-06-25T11:50:22.2281207Z       |                         ^~~~~~~
2026-06-25T11:50:22.2328883Z       |                         mkdtemp
2026-06-25T11:50:22.2331570Z In file included from ./boost/test/included/unit_test.hpp:20,
2026-06-25T11:50:22.2348848Z                  from D:/a/test/boost-root/libs/test/doc/examples/runtime-configuration_2.run-fail.cpp:10:
2026-06-25T11:50:22.2385333Z ./boost/test/impl/debug.ipp: In function 'void boost::debug::debugger_break()':
2026-06-25T11:50:22.2387231Z ./boost/test/impl/debug.ipp:753:7: error: '::kill' has not been declared
2026-06-25T11:50:22.2393802Z   753 |     ::kill( ::getpid(), SIGTRAP );
2026-06-25T11:50:22.2412712Z       |       ^~~~
2026-06-25T11:50:22.2414959Z ./boost/test/impl/debug.ipp: In function 'bool boost::debug::attach_debugger(bool)':
2026-06-25T11:50:22.2416643Z ./boost/test/impl/debug.ipp:935:36: error: '::mkstemp' has not been declared; did you mean 'mkdtemp'?
2026-06-25T11:50:22.2417786Z   935 |     fd_holder init_done_lock_fd( ::mkstemp( init_done_lock_fn ) );
2026-06-25T11:50:22.2418626Z       |                                    ^~~~~~~
2026-06-25T11:50:22.2419285Z       |                                    mkdtemp
2026-06-25T11:50:22.2420149Z ./boost/test/impl/debug.ipp:973:11: error: '::select' has not been declared
2026-06-25T11:50:22.2421043Z   973 |         ::select( 0, 0, 0, 0, &to );
2026-06-25T11:50:22.2421672Z       |           ^~~~~~
2026-06-25T11:50:22.2422175Z 

I can disable cygwin CI here if you don't want to fix this.

[mborland]

Disable it for now and if there's demand in the future I can go back and fix it. If it's been this long and nobody has complained I would expect nobody uses it.

Edit: It looks like it's been over 6 years since the last real change to that file