chore(ci): Use hashbrown 0.15.0 in MSRV check #503

Job	Run time
Check Style	11s
semver	21s
features	40s
Check MSRV (1.63)	1m 29s
Test with Miri	45s
Test stable on ubuntu-latest	36s
Test stable on windows-latest	1m 34s
Test stable on macos-latest	28s
Test beta on ubuntu-latest	33s
Test beta on windows-latest	1m 13s
Test beta on macos-latest	32s
Test nightly on ubuntu-latest	32s
Test nightly on windows-latest	1m 18s
Test nightly on macos-latest	47s
Build docs	18s
CI is green	0s
	11m 17s

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