Update gitattributes for test data

The test data should not be modified, regardless of host and settings

Signed-off-by: Joshua Lock <jlock@vmware.com>

Author: joshuagl

.gitattributes

@@ -1,3 +1,2 @@
-# All JSON files will always have LF line endings on checkout.
-# This prevents git replacing line endings with CRLF on Windows.
-*.json text eol=lf
+# Test data should not be modified on checkout, regardless of host settings
+*.json binary