When using hosted runners in combination with cached docker images,
there is the possibility that the host runner image is updated,
rendering the linux-headers package (stored in the cached docker image)
incompatible.
Fix this by doing a re-install of the headers package in
03_test_script.sh.
If the underlying runner kernel has not changed thie has no effect, but
prevents the job from failing if it has.
2c990d84a3