tools/make_pip: Use venv when invoking pip

Recent Ubuntu versions (24.04+) disallow pip by default when
installing packages. The recommended approach is to use a virtual
environment (venv) instead.
Because of this, "make pip" is failing on such versions.

To prepare CI container migration to Ubuntu 24.04, use a venv in the
make_pip script.

Note: This has been reported on [1]

[1] https://source.denx.de/u-boot/custodians/u-boot-dm/-/issues/37

Signed-off-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>
1 file changed