(cd repo1 && bazel run //python/test:test)
passes.
(cd repo2 && bazel run //python/test:test)
passes.
Comment / uncomment the load in repo1/python/BUILD.bazel
(cd repo2 && bazel run //python/test:test)
now fails and the sys.path does not contain repo1 anymore.
Unfortunately, it seems with rules_py imports do not "properly cross repos".