Changes

Using actions/checkout@v2 to checkout the github code onto your local workspace is nice, but can be problematic when using old docker image. From what I understand, the action uses NodeJS version internally and therefore requires a modern glibc version as the action can impose newer NodeJS version and therefore can eventually break our build.

To avoid this, I'm just going to manually checkout the code and run the submodule update manually. This will fix our C builds.