Ensure rustfmt is invoked without edition parameter #298

Job	Run time
test (ubuntu-latest, 28.2)	49s
test (ubuntu-latest, 26.3)	39s
test (ubuntu-latest, 27.2)	48s
test (macos-latest, 30.1)	4m 5s
test (ubuntu-latest, 29.4)	1m 37s
test (windows-latest, 26.3)	2m 36s
test (ubuntu-latest, 30.1)	1m 24s
test (macos-latest, snapshot, true)	3m 17s
test (macos-latest, 29.4)	3m 31s
test (windows-latest, 28.2)	2m 12s
test (windows-latest, 27.2)	2m 31s
test (macos-latest, 28.2)	3m 26s
test (windows-latest, 30.1)	2m 48s
test (ubuntu-latest, snapshot, true)	44s
test (windows-latest, snapshot, true)	1m 41s
test (windows-latest, 29.4)	1m 58s
	34m 6s

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