Do not explicitly begin() a transaction.

This code is raising an InvalidRequestError.

packit_service/models.py

@@ -23,7 +23,6 @@
 
 from cachetools import TTLCache, cached
 from cachetools.func import ttl_cache
-from packit.config import JobConfigTriggerType
 from sqlalchemy import (
     JSON,
     Boolean,
@@ -55,6 +54,7 @@
 from sqlalchemy.sql.functions import count
 from sqlalchemy.types import ARRAY
 
+from packit.config import JobConfigTriggerType
 from packit_service.constants import ALLOWLIST_CONSTANTS
 
 logger = logging.getLogger(__name__)
@@ -2342,8 +2342,6 @@ 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