Avoid using io_bazel directly

Working towards https://github.com/bazelbuild/bazel/issues/18957

RELNOTES: None
PiperOrigin-RevId: 562743741
Change-Id: Iaef46f0a67d264968f399805da7f5cf9566cb035
diff --git a/scripts/docs/rewriter_test.py b/scripts/docs/rewriter_test.py
index 731eeeb..b13cece 100644
--- a/scripts/docs/rewriter_test.py
+++ b/scripts/docs/rewriter_test.py
@@ -34,7 +34,9 @@
 
 def read_data_file(basename, in_or_out_fragment):
   path = os.path.join(
-      os.getenv("TEST_SRCDIR"), "io_bazel/scripts/docs/testdata",
+      os.getenv("TEST_SRCDIR"),
+      os.getenv("TEST_WORKSPACE"),
+      "scripts/docs/testdata",
       in_or_out_fragment, basename)
   with open(path, "rt", encoding="utf-8") as f:
     return path, f.read()