fix: fix android header title font weight (#7720)
fix: fix android header title font weight (#7720)

the previously used fort weight of 500 would effectively be converted to `fontWeight: bold` because of https://github.com/facebook/react-native/pull/25341

this fixes the title appearance to look as customary

react-community/react-navigation,react-community/react-navigation,react-community/react-navigation