Add comprehensive tests for object tag-based policy conditions:
- TestExistingObjectTagCondition: Basic tag matching scenarios
- Matching/non-matching tag values
- Missing tags, no tags, empty tags
- Multiple tags with one matching
- TestExistingObjectTagConditionMultipleTags: Multiple tag conditions
- Both tags match
- Only one tag matches
- TestExistingObjectTagDenyPolicy: Deny policies with tag conditions
- Default allow without tag
- Deny when specific tag present