Fix test to skip when changelog_entry.yaml is empty

The versioning workflow consumes changelog_entry.yaml, leaving it empty.
This causes the test to fail on the next CI run. Add skip logic for
empty files to prevent this.

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

Co-Authored-By: Claude <noreply@anthropic.com>

Author: MaxGhenis

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+      - Fix changelog encoding test to skip when changelog_entry.yaml is empty after versioning

policyengine_uk_data/tests/test_changelog_encoding.py

@@ -34,6 +34,10 @@ def test_changelog_entry_is_valid_utf8(self):
         # Read as bytes and try to decode as UTF-8
         content_bytes = changelog_entry_path.read_bytes()
 
+        # Skip if file is empty (happens after versioning workflow consumes it)
+        if not content_bytes.strip():
+            pytest.skip("changelog_entry.yaml is empty")
+
         try:
             content_bytes.decode("utf-8")
         except UnicodeDecodeError as e:
@@ -56,11 +60,19 @@ def test_changelog_entry_is_valid_yaml(self):
 
         content = changelog_entry_path.read_text(encoding="utf-8")
 
+        # Skip if file is empty (happens after versioning workflow consumes it)
+        if not content.strip():
+            pytest.skip("changelog_entry.yaml is empty")
+
         try:
             data = yaml.safe_load(content)
         except yaml.YAMLError as e:
             pytest.fail(f"changelog_entry.yaml is not valid YAML: {e}")
 
+        # Skip if data is None (empty YAML)
+        if data is None:
+            pytest.skip("changelog_entry.yaml is empty")
+
         # Verify structure
         assert isinstance(data, list), "changelog_entry.yaml must be a list"
         for entry in data: