CI: Update GitHub actions to modern versions

[joncinque]

Problem

Our GitHub Actions runs produce loads of warnings because we're using old versions of actions or deprecated actions.

Solution

Update them all! Everything was done in separate commits, but here's the list:

• actions/checkout -> v4
• actions/cache -> v3
• actions/upload-artifact -> v3
• actions/download-artifact -> v3
• actions/setup-node -> v4
• actions-rs/toolchain -> dtolnay/rust-toolchain which seems to be the next version used by everyone, maintained by a Rust OG
• actions-rs/cargo -> just call cargo
• actions-rs/install -> just call cargo install

[buffalojoec]