Set `shell: bash` by default on all workflows #4941

Job	Run time
Diagnostic export (windows-latest, linked)	2m 58s
Diagnostic export (macos-latest, linked)	57s
Diagnostic export (ubuntu-latest, linked)	1m 0s
Diagnostic export (macos-latest, nightly-latest)	1m 0s
Diagnostic export (ubuntu-latest, nightly-latest)	1m 3s
Diagnostic export (windows-latest, nightly-latest)	2m 22s
	9m 20s

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