Reverted to actions/checkout@v3 to deal with old node versions

[COM8]

Compiling with older versions of Ubuntu (e.g. 18.04) results in:

Run actions/checkout@v4
/usr/bin/docker exec  4567e21c9cc6600b4ad85f7a41819a3b13ac0ee1deff34facae87e11fddf53d6 sh -c "cat /etc/*release | grep ^ID"
/__e/node20/bin/node: /lib/x86_64-linux-gnu/libc.so.6: version `GLIBC_2.28' not found (required by /__e/node20/bin/node)

Ref: actions/checkout#1487

As a solution we revert back to v3 of actions/checkout.