ci: default to bash shell #507

Job	Run time
Test (macOS-latest)	5m 36s
Test (ubuntu-24.04)	8m 4s
Test (windows-2022)	14m 32s
Compiletest (ubuntu-24.04)	6m 16s
Android (ubuntu-24.04, aarch64-linux-android)	8m 3s
Compiletest (windows-2022)	11m 6s
Compiletest (macOS-latest)	5m 13s
cargo-deny	57s
Difftest (ubuntu-24.04)	8m 43s
Lint	6m 16s
Difftest (macOS-latest)	5m 11s
Difftest (windows-2022)	15m 37s
test_success	3s
	1h 35m 37s

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