gh-128690: temporarily do not use test_embed in PGO profile builds

[ned-deily]

As documented in #128690, under certain configurations test case test_init_pyvenv_cfg of test_embed fails apparently since 34e840f. This behavior was not seen in 3.14.0a3, the most recent alpha before this change. Unfortunately, test_embed is included in the subset of tests used for PGO profile builds when Python is built with --enable-optimizations. If any of the tests included in the PGO profile build fails, including test_embed, the whole Python build fails. Besides the originally reported case, I have now seen this failure in two other macOS build configurations, both rather complex; one is for the build of the python.org installer package. (At the moment, I haven't had time to produce a manageable reproducible test case.) It could be that this is just an existing test case issue that was brought to the fore by the above change. Since the failure involves sys._base_executable, it's possible that the behavior documented in #128670 might be the root cause.

If necessary for 3.14.0a4, I could apply this PR manually to avoid using test_embed in the profile builds. But I would prefer to either have the test failure resolved prior to a4 or merge this PR to temporarily avoid using test_embed. Marking as release-blocker for release manager decision.

cc: @hugovk @FFY00

• Issue: test_embed.test_init_pyvenv_cfg() fails #128690

[hugovk]

I'm fine with this for a4, especially if it's temporary, and I guess it won't make too much difference to the PGO build.