Set `shell: bash` by default on all workflows #4940

Job	Run time
Diagnostic export (ubuntu-latest, linked)	1m 4s
Diagnostic export (macos-latest, nightly-latest)	1m 29s
Diagnostic export (windows-latest, linked)	2m 39s
Diagnostic export (windows-latest, nightly-latest)	2m 38s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 0s
Diagnostic export (macos-latest, linked)	59s
	9m 49s

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