[ibm-db] Add stubs for ibm_db_ctx (#15463)

stubs/ibm-db/ibm_db_ctx.pyi

@@ -0,0 +1,8 @@
+from types import TracebackType
+
+import ibm_db
+
+class Db2connect:
+    def __init__(self, dsn: str, username: str, password: str) -> None: ...
+    def __enter__(self) -> ibm_db.IBM_DBConnection: ...
+    def __exit__(self, t: type[BaseException] | None, v: BaseException | None, tb: TracebackType | None) -> None: ...