CI: kernel: generate ccache cache on kernel push

CI: kernel: generate ccache cache on kernel push

To actually use ccache cache on kernel test from pr, the kernel workflow
has to be run first from a push action.

This will permit as a side effect to test merged commits and catch commit
that may cause regression in kernel compilation even outside the github
system.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>