dockerized_execution: Clean broken .cache folder references

Running dockerized tests while having bazel cache references in your
repository folder could lead to errors like this:
"<path> is not in the subpath of '/git'"

This change fixes that by removing any broken links to this
.cache folder of the base host from the mounted repository root.

Change-Id: Ib0c82d588f67d3b261d55103d0b37d10524f3d83
(cherry picked from commit 6807202482a4ab83c11f6343cac789d4ef8e868e)

tests/testlib/script_helpers/dockerized_execution.py

@@ -731,6 +731,9 @@ def _prepare_git_overlay(
         ],
     )
 
+    # remove any broken links in the repository (e.g. invalid bazel cache references)
+    _exec_run(container, ["find", target_path, "-maxdepth", "1", "-xtype", "l", "-delete"])
+
     # target_path belongs to root, but its content belong to testuser. Newer git versions don't like
     # that by default, so we explicitly say that this is ok.
     _exec_run(