fix: disable gpg signing in test git fixtures and skip root-only permission test

Test fixtures that create temporary git repos now set commit.gpgsign=false
to avoid failures in environments with global commit signing configured.
The permission error test is skipped when running as root since file
permissions don't apply to the root user.

https://claude.ai/code/session_018u1fAx2GihSGctYS64tD4H

tests/self_coding/test_self_coding_integration.py

@@ -39,7 +39,11 @@ def self_coding_env():
             ["git", "config", "user.name", "Test User"],
             cwd=repo_path, check=True, capture_output=True,
         )
-        
+        subprocess.run(
+            ["git", "config", "commit.gpgsign", "false"],
+            cwd=repo_path, check=True, capture_output=True,
+        )
+
         # Create src directory with real Python files
         src_path = repo_path / "src" / "myproject"
         src_path.mkdir(parents=True)