chore(ci): Use hashbrown 0.15.0 in MSRV check #504

Job	Run time
semver	24s
Check Style	15s
Test with Miri	46s
Check MSRV (1.63)	1m 50s
Test stable on ubuntu-latest	36s
features	43s
Test stable on windows-latest	2m 1s
Test stable on macos-latest	29s
Test beta on ubuntu-latest	35s
Test beta on windows-latest	1m 16s
Test beta on macos-latest	32s
Test nightly on ubuntu-latest	33s
Test nightly on windows-latest	1m 20s
Test nightly on macos-latest	39s
Build docs	16s
CI is green	1s
	12m 16s

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