Fix git encoding issues with encoding test files

Mark wrongenc.inc files as binary in .gitattributes to prevent encoding
conversion issues on different platforms. These files contain intentional
Latin-1 encoded content for testing Sphinx's encoding handling and should
remain byte-for-byte identical.

Fixes git errors like:
- "failed to encode from UTF-8 to latin-1"
- stash/unstash failures with these files

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <[email protected]>

Author: ianhi

.gitattributes

@@ -51,8 +51,11 @@ tests/roots/test-pycode/cp_1251_coded.py dos
 
 # Non UTF-8 encodings
 tests/roots/test-pycode/cp_1251_coded.py working-tree-encoding=windows-1251
-tests/roots/test-root/wrongenc.inc working-tree-encoding=latin-1
-tests/roots/test-warnings/wrongenc.inc working-tree-encoding=latin-1
+
+# Encoding test files - treated as binary to prevent encoding conversion issues
+# These files contain intentional Latin-1 encoded content for testing Sphinx's encoding handling
+tests/roots/test-root/wrongenc.inc binary
+tests/roots/test-warnings/wrongenc.inc binary
 
 # Generated files
 # https://github.com/github/linguist/blob/master/docs/overrides.md