Update RxSwift version to 6.5.0

[sk-chanch]

update swift package rxswift to 6.5.0

[ashfurrow]

Hi! Thanks for the pull request and your patience while I respond. This change makes sense – we should update the CocoaPod podspec before releasing a new version, but I can take care of that.

[DivineDominion]

I'm closing this because we had no activity on this for almost 3 years and RxSwift received more updates in the meantime.

In general, we don't need to bump the version as long as there's no backwards-compatibility breaking change, in which case RxOptional major version should also be bumped: we can reduce maintenance overhead by removing the Package.resolved #113 instead and let users decide which library versions they want to bundle. (It's almost always "the very latest releases" anyway, except when it isn't and versions need to be pinned :))

Thanks for the suggestion, though!