Add `getOptionalEnvVar` helper #6126

Job	Run time
Go: tracing with legacy workflow (macos-latest, stable-v2.17.6)	6m 45s
Go: tracing with legacy workflow (ubuntu-latest, stable-v2.22.4)	1m 18s
Go: tracing with legacy workflow (macos-latest, stable-v2.22.4)	4m 53s
Go: tracing with legacy workflow (macos-latest, stable-v2.21.4)	4m 52s
Go: tracing with legacy workflow (ubuntu-latest, stable-v2.20.7)	1m 31s
Go: tracing with legacy workflow (ubuntu-latest, stable-v2.21.4)	1m 26s
Go: tracing with legacy workflow (ubuntu-latest, default)	1m 34s
Go: tracing with legacy workflow (macos-latest, stable-v2.19.4)	6m 26s
Go: tracing with legacy workflow (macos-latest, stable-v2.18.4)	5m 54s
Go: tracing with legacy workflow (ubuntu-latest, stable-v2.18.4)	1m 19s
Go: tracing with legacy workflow (ubuntu-latest, stable-v2.19.4)	1m 20s
Go: tracing with legacy workflow (ubuntu-latest, stable-v2.17.6)	1m 32s
Go: tracing with legacy workflow (macos-latest, stable-v2.20.7)	6m 14s
Go: tracing with legacy workflow (macos-latest, default)	6m 2s
Go: tracing with legacy workflow (macos-latest, linked)	6m 42s
Go: tracing with legacy workflow (ubuntu-latest, linked)	1m 13s
Go: tracing with legacy workflow (ubuntu-latest, nightly-latest)	1m 24s
Go: tracing with legacy workflow (macos-latest, nightly-latest)	6m 21s
	1h 6m 46s

Provide feedback