Add Emscripten test skips for recently added tests.

[freakboy3742]

Some minor changes to some tests that recently started failing on Emscripten:

• Tests from gh-135953: Add GIL contention markers to sampling profiler Gecko format #139485 that can't run on Emscripten because of the lack of threads
• A tweak to how free-threading is detected in the profiler tests, matching other usages (because an environment variable value of Py_GIL_DISABLED=0 shouldn't be interpreted as "GIL disabled") Not sure what is going on with this one, but it caused all the Windows and Ubuntu tests to fail.
• A test that now fails as a result of a change made by Implement stack overflow protection for linux based on actual stack depth #130396

[freakboy3742]

!buildbot emscripten

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @freakboy3742 for commit 1118f6f 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F143551%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

• WASM Emscripten PR

[freakboy3742]

!buildbot emscripten

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @freakboy3742 for commit 9c4d800 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F143551%2Fmerge

The command will test the builders whose names match following regular expression: emscripten

The builders matched are:

• WASM Emscripten PR

[vstinner]

LGTM. I didn't test the change, I just read the code changes.

[hoodmane]

Thanks @freakboy3742 !