chore: Release rexpect version 0.6.4 #319

Job	Run time
clippy	34s
rustfmt	15s
Test (ubuntu-latest, stable)	22s
Check MSRV (ubuntu-latest)	21s
Coverage	29s
Minimal versions (ubuntu-latest)	31s
Docs	23s
lockfile	22s
CI	2s
	3m 19s

Provide feedback