gitlab-ci: fix "msvc-meson" test job succeeding despite test failures

We have recently noticed that the "msvc-meson" test job in GitLab CI
succeeds even if there are failures. This is somewhat puzzling because
we use exactly the same command as we do on GitHub Actions, and there
the jobs fail as exected.

As it turns out, this is another weirdness of the GitLab CI hosted
runner for Windows [1]: by default, even successful commands will not
make the job fail. Interestingly though, this depends on what exactly
the command is that you're running -- the MinGW-based job for example
works alright and does fail as expected.

The root cause here seems to be specific behaviour of PowerShell. The
invocation of `ForEach-Object` does not bubble up any errors in case the
invocation of `meson test` fails, and thus we don't notice the error.
This is specific to executing the command in a loop: other build steps
where we execute commands directly fail as expected.

This is because the specific version of PowerShell that we use in the
runner does not know about `PSNativeCommandUseErrorActionPreference`
yet, which controls whether native commands like "meson.exe" honor the
`ErrorActionPreference` variable. The preference has been introduced
with PowerShell 7.3 and is default-enabled since PowerShell 7.4, but
GitLab's hosted runners still seem to use PowerShell 5.1. Consequently,
when tests fail, we won't bubble up the error at all from the loop and
thus the job doesn't fail. This isn't an issue in other cases though
where we execute native commands directly, as the GitLab runner knows to
check the last error code after every command.

The same thing doesn't seem to be an issue on GitHub Actions, most
likely because it uses PowerShell 7.4. Curiously, the preference for
`PSNativeCommandUseErrorActionPreference` is disabled there, but the
jobs fail as expected regardless of that. It's puzzling, but I do not
have enough PowerShell expertise to give a definitive answer as to why
it works there.

In any case, Meson 1.8 will likely get support for slicing tests [1], so
we can eventually get rid of the whole PowerShell script. For now, work
around the issue by explicitly exiting out of the loop with a non-zero
error code if we see that Meson has failed.

[1]: https://github.com/mesonbuild/meson/pull/14092

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>