CI: add ~/.local/bin to PATH (Linux only)

CI: add ~/.local/bin to PATH (Linux only)

Without adding ~/.local/bin to PATH, `pip install` will throw
an error when running inside a container.
Containers will be introduced to the CI in the following commits.

Signed-off-by: Oliver Steffen <osteffen@redhat.com>
Reviewed-by: Michael Kubacki <michael.kubacki@microsoft.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Acked-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Chris Fernald <chfernal@microsoft.com>