Ubuntu job should install gdb

[vstinner]

test_gdb is skipped on the GitHub Action Ubuntu job, because gdb is not installed.

Would it be possible to install it?

I broke buildbots because I renamed the function "collect" to "gc_collect_main" in Modules/gcmodule.c and python-gdb.py uses it to check if Python is running a garbage collection. The strange thing is that test_gdb passed on Travis CI of my PR python/cpython#23038 test_gdb was skipped on the Ubuntu job.

[brettcannon]

You can install whatever you want as you have full access to the running container through passwordless sudo. Add a step to install gdb (and anything else you want) to the appropriate job and that should do it.

[vstinner]

I created python/cpython#23043 to add gdb dependency. Let's see if test_gdb is still skipped or nor.

[vstinner]

Fixed in 3.9 and master, 3.8 is going to be fixed as soon as the CI tests pass.