chore(ci): pin hashbrown for MSRV job #2913

Job	Run time
Check Style	3s
Verify hyper.h is up to date	19s
Test with Miri	2m 8s
Test C API (FFI)	25s
features	30s
Check deprecated on stable	9s
Check MSRV (1.63)	53s
Check deprecated on beta	19s
Test stable on ubuntu-latest	1m 17s
Test stable on windows-latest	3m 24s
Test stable on macOS-latest	1m 31s
Test beta on ubuntu-latest	1m 27s
Test beta on windows-latest	2m 33s
Test beta on macOS-latest	1m 25s
Test nightly on ubuntu-latest	1m 20s
Test nightly on windows-latest	2m 42s
Test nightly on macOS-latest	1m 26s
Build docs	21s
CI is green	1s
	22m 13s

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