buildGoModule: pre-initialize module cache (#61967)

For some Go projects a go.mod file is included but there are no listed
dependencies. When this is encountered the Go toolchain will not create
a cache folder for downloaded dependencies which causes buildGoModule to
fail.

An example of a project like this that is widely used is:
https://github.com/golang/protobuf

This commit adds a mkdir command to ensure that the directory always
exists so it can be copied and prevent the failure.