python: Install pygdbmi in meson's venv

python: Install pygdbmi in meson's venv

The upcoming changes in the reverse_debugging functional test to remove
Avocado as a dependency will require pygdbmi for interacting with GDB,
so install it in meson's venv (located in the build dir's pyvenv/).

Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Gustavo Romero <gustavo.romero@linaro.org>
Message-ID: <20251003141820.85278-3-gustavo.romero@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>