style: fix lint errors in test files

Why this change is needed:
CI reported 5 lint errors that needed to be fixed:
- Unused import of 'patch' in test_dimension_mismatch.py
- Unnecessary f-string prefixes without placeholders
- Bare except clauses without exception type

How it solves it:
- Removed unused 'patch' import (auto-fixed by ruff)
- Removed unnecessary f-string prefixes (auto-fixed by ruff)
- Changed bare 'except:' to 'except Exception:' for proper exception handling

Impact:
- Code now passes all ruff lint checks
- Better exception handling practices (doesn't catch SystemExit/KeyboardInterrupt)
- Cleaner, more maintainable test code

Testing:
Verified with: uv run ruff check tests/
Result: All checks passed!

tests/test_dimension_mismatch.py

@@ -7,7 +7,7 @@ legacy collections/tables to new ones with different embedding models.
 """
 
 import pytest
-from unittest.mock import MagicMock, AsyncMock, patch
+from unittest.mock import MagicMock, AsyncMock
 
 from lightrag.kg.qdrant_impl import QdrantVectorDBStorage
 from lightrag.kg.postgres_impl import PGVectorStorage

tests/test_e2e_multi_instance.py

@@ -1153,7 +1153,7 @@ async def test_dimension_mismatch_postgres(
                 },
             )
 
-        print(f"✅ Legacy table created with 3 records (1536d)")
+        print("✅ Legacy table created with 3 records (1536d)")
 
         # Step 2: Try to initialize LightRAG with NEW model (3072d)
         async def embed_func_new(texts):
@@ -1271,7 +1271,7 @@ async def test_dimension_mismatch_qdrant(
         # Delete if exists
         try:
             client.delete_collection(legacy_collection)
-        except:
+        except Exception:
             pass
 
         # Create legacy collection with 768d
@@ -1294,7 +1294,7 @@ async def test_dimension_mismatch_qdrant(
             )
 
         client.upsert(collection_name=legacy_collection, points=points, wait=True)
-        print(f"✅ Legacy collection created with 3 records (768d)")
+        print("✅ Legacy collection created with 3 records (768d)")
 
         # Step 2: Try to initialize LightRAG with NEW model (1024d)
         async def embed_func_new(texts):
@@ -1384,7 +1384,7 @@ async def test_dimension_mismatch_qdrant(
             for coll in client.get_collections().collections:
                 if "lightrag" in coll.name.lower():
                     client.delete_collection(coll.name)
-        except:
+        except Exception:
             pass