Add Heimdal test file test_base.c to bi-directional encoding ignore list

Heimdal commit c6a46f0c96dde73ef4f3a247a1e904d4cf15aeb2 introduces test data
that triggers our LTR and RTL detection code.

Signed-off-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Joseph Sutton <josephsutton@catalyst.net.nz>

python/samba/tests/source_chars.py

@@ -110,6 +110,7 @@ SAFE_FORMAT_CHARS = {
 # In the real world mixing directions would be normal in bilingual
 # documents, but it is rare in Samba source code.
 BIDI_FILES = {
+    'third_party/heimdal/lib/base/test_base.c',
     'third_party/heimdal/lib/wind/NormalizationTest.txt',
     'testdata/source-chars-bidi.py',
 }