chore: annotate testing binaries (OSSF scorecard) (#4472)

OpenSSF scorecard currently complains about our binary files.  This adds an
annotation explaining what's in them and why we have them in case anyone's curious.

Signed-off-by: Terri Oda <[email protected]>

Author: terriko

.github/scorecard.yml

@@ -0,0 +1,5 @@
+annotations:
+  - checks:
+      - binary-artifacts
+    reasons:
+      - reason: test-data # binary files for testing binary scanner. Most are text signatures with no code.