Cannot upgrade to checkout/actions@v4 due to min required GLIBC version

[ximon18]

See: https://github.com/actions/checkout/issues/1487

This affects runs of the pkg and pkg-test jobs on older O/S versions such as Ubuntu Bionic or CentOS 7 such that the action fails to run.

An example failure can be seen here: https://github.com/NLnetLabs/ploutos-testing/actions/runs/7003880244/job/19051158702#step:3:1

> Run actions/checkout@v4
/usr/bin/docker exec  0780bbc959b43dd45f9e9f5e1b8bab49ba0eb0f791b831e32536aa5c7a2aa70b 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)