build-unit-test-docker: sdbusplus: use pip for install

Currently sdbusplus uses a setup.py, which is a deprecated method
for installing python packages.  If we use `pip` here, we can allow
it to detect how sdbusplus specifies its installation directives,
which will allow transition from the older setup.py to newer
pyproject.toml method.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Ie956fc32972f4e0ef225a1f8c04d98642098b6a2
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 77b734c..a1e0312 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -293,7 +293,7 @@
         build_type="meson",
         custom_post_dl=[
             "cd tools",
-            f"./setup.py install --root=/ --prefix={prefix}",
+            "python3 -m pip install --break-system-packages --root-user-action ignore .",
             "cd ..",
         ],
         config_flags=[