Enable signing without private key #1542

Job	Run time
build-windows	12m 53s
build (macOS-latest, stable)	4m 20s
Validate external types appearing in public API	1m 33s
build (ubuntu-latest, stable)	5m 38s
Build rustls-cert-gen as a standalone package	30s
build (ubuntu-latest, beta)	5m 29s
Measure coverage	5m 25s
build (ubuntu-latest, nightly)	5m 37s
Format & clippy	5m 8s
build (ubuntu-latest, stable 7 months ago)	5m 42s
Documentation (stable)	56s
Documentation (nightly)	1m 4s
Check semver compatibility	54s
	55m 9s

Provide feedback