build-unit-test-docker: Don't generate markdown for PDI

Not used in the unit test container.

Change-Id: I19c053bf73cd08b19f30c855191f1f087f8bca1c
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/scripts/build-unit-test-docker b/scripts/build-unit-test-docker
index 301fc1f..1cf714b 100755
--- a/scripts/build-unit-test-docker
+++ b/scripts/build-unit-test-docker
@@ -201,6 +201,7 @@
     "openbmc/phosphor-dbus-interfaces": PackageDef(
         depends=["openbmc/sdbusplus"],
         build_type="meson",
+        config_flags=["-Dgenerate_md=false"],
     ),
     "openbmc/phosphor-logging": PackageDef(
         depends=[