wallet: Bump bitcoin dependency to v0.32.4

[stevenroose]

This is required since we are using Network::Testnet4

Changelog notice

bdk_wallet:

• deps: Bump bitcoin to 0.32.4

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

[ValuedMammal]

ACK 5553e8d

[notmandatory]

ACK 5553e8d

[evanlinjin]

Why is this required? It's a patch release of bitcoin so it should have happened automatically if you do cargo update in your project? I don't see the reason to force users to a later patch version (unless if there is a critical bug fix).