Use transaction context manager

This code is raising an InvalidRequestError.

packit_service/models.py

@@ -2341,33 +2341,31 @@ def add_scan_transaction(self) -> Generator["OSHScanModel"]:
 
         raise: IntegrityError if the scan model already exists
         """
-        session = singleton_session or Session()
-        session.begin()
-
-        try:
-            scan = OSHScanModel()
-            scan.copr_build_target = self
-            session.add(scan)
-            session.commit()
-        except Exception as ex:
-            logger.warning(f"Exception while working with database: {ex!r}")
-            session.rollback()
-            raise
-
-        try:
-            yield scan
-        except Exception as ex:
-            logger.warning(f"{ex!r}")
-            session.rollback()
-            raise
-
-        try:
-            session.add(scan)
-            session.commit()
-        except Exception as ex:
-            logger.warning(f"Exception while working with database: {ex!r}")
-            session.rollback()
-            raise
+        with sa_session_transaction() as session:
+            try:
+                scan = OSHScanModel()
+                scan.copr_build_target = self
+                session.add(scan)
+                session.commit()
+            except Exception as ex:
+                logger.warning(f"Exception while working with database: {ex!r}")
+                session.rollback()
+                raise
+
+            try:
+                yield scan
+            except Exception as ex:
+                logger.warning(f"{ex!r}")
+                session.rollback()
+                raise
+
+            try:
+                session.add(scan)
+                session.commit()
+            except Exception as ex:
+                logger.warning(f"Exception while working with database: {ex!r}")
+                session.rollback()
+                raise
 
 
 class KojiBuildGroupModel(ProjectAndEventsConnector, GroupModel, Base):