Update rustls-platform-verifier requirement from 0.3 to 0.4 #555

Job	Run time
Build+test (stable, ubuntu-latest)	3m 30s
Build+test (beta, ubuntu-latest)	2m 47s
msrv	56s
Build+test (nightly, ubuntu-latest)	3m 31s
Build+test (macos-latest, stable)	2m 40s
Check for documentation errors	21s
Clippy	54s
Build+test (windows-latest, stable)	5m 3s
features	1m 42s
Format	10s
Check semver compatibility	1m 0s
	22m 34s

Provide feedback