Upgrade to `actions/checkout@v4` in GitHub Actions. (#486) #1328

Job	Run time
Check lint and rustfmt	57s
Run tests	1m 52s
Check fuzz targets	28s
Check rustdoc WASM target	24s
Run JS linters	2m 23s
pre-publish checks	18s
WASM tests	19s
Python tests and maturin build (3.9)	16s
Python tests and maturin build (3.10)	19s
Python tests and maturin build (3.11)	21s
Python tests and maturin build (3.12)	15s
All CI stages	1s
pre-publish checks	1s
publish trustfall_filetests_macros	1s
publish trustfall_core	1s
publish trustfall_derive	1s
publish python trustfall	1s
publish trustfall	1s
publish trustfall_stubgen	1s
	8m 0s

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