Bump rust version for cross-compatibility tests #4495

Job	Run time
check feature flags (ubuntu-latest / stable)	16m 55s
check format (ubuntu-latest / nightly)	11s
check examples (ubuntu-latest / stable)	43s
check docs (ubuntu-latest / stable)	58s
check licenses (ubuntu-latest / stable)	23s
check linter (ubuntu-latest / stable)	1m 21s
check minimal versions of transitive dependencies (ubuntu-latest / stable)	24s
check minimal supported rust version (ubuntu-latest / msrv)	24s
check spelling (ubuntu-latest / nightly)	3m 44s
test (ubuntu-latest / stable)	7m 31s
test (macos-latest / stable)	8m 54s
test (windows-latest / stable)	10m 54s
	52m 22s

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