Gate rustc on both Azure and (GitHub Actions - macOS)

[tmiasko]

Gate rustc CI on both Azure and GitHub Actions with the exception of macOS
builders to quickly detect builds that will inevitably fail on Azure, while
avoiding spurious failures described in rust-lang/rust#71988.

Time to failure (TTF) on Azure and GitHub Actions (GHA) from a few different
rollups (measurements for GHA include non-spurious failures from macOS builders
under simplifying assumption that they would also fail elsewhere around the
same time):

Rollup	Azure TTF	GHA TTF
73271	1h 48m 1s	22m 4s
73240	1h 7m 30s	23m 52s
73231	2h 22m 45s	25m 48s
73168	1h 50m 34s	23m 41s
73064	2h 19m 42s	42m 13s
73062	1h 58m 42s	41m 24s
73053	2h 5m 57s	37m 32s

Potential drawbacks: increased likelihood of spurious failures.

[pietroalbini]

That's a great point! Added this to this week's infrastructure team meeting.

[tmiasko]

Blocked on recently introduced failures on arm-android & GitHub Actions rust-lang/rust#73535.