fix: python bindings: install on Debian python >= 3.10

fix: python bindings: install on Debian python >= 3.10

Starting with Debian's Python 3.10, the default install scheme is
'posix_local' which is a Debian specific scheme based on 'posix_prefix'
but with an added 'local' prefix. This is the default so users doing
system wide manual installations of python modules end up in
'/usr/local'. This interferes with our autotools based install which
already defaults to '/usr/local' and expects a provided prefix to be
used verbatim.

Monkeypatch sysconfig to override this scheme and use 'posix_prefix'
instead.

Change-Id: I41973f6db4966519aa1c7e74a9d1e9b5d90bf7ea
Signed-off-by: Michael Jeanson <mjeanson@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/10343
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>