python: ctx: Ensure we are holding the GIL

python: ctx: Ensure we are holding the GIL

This is required because we usally return the GIL when we are jumping
into Pakfire functions as these tend to take some time when running.

When we are jumping back into the Python code, we need to acquire the
GIL again.

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>