update actions/checkout from v3 to v4

[Daulox92]

Updates all instances of actions/checkout@v3 to actions/checkout@v4

Reference:
Latest version confirmation: https://github.com/actions/checkout/releases/tag/v4.2.2

[tcharding]

ACK beeed10

[tcharding]

Thanks

[apoelstra]

@Daulox92 can you add a commit to the beginning of this PR by running cargo +nightly clippy --all-features --all-targets and fixing all the lints that pop up? There aren't a lot and they're pretty trivial but they're preventing me from passing my local test script.

[Daulox92]

@Daulox92 can you add a commit to the beginning of this PR by running cargo +nightly clippy --all-features --all-targets and fixing all the lints that pop up? There aren't a lot and they're pretty trivial but they're preventing me from passing my local test script.

@apoelstra Could you help with running clippy and fixing these issues? I don't have the proper Rust environment set up at the moment.