When interrupted with Ctrl+C, exit code should be 1 not 0

src/qlever/qlever_main.py

@@ -43,7 +43,7 @@ def main():
         log.info("")
         log.info("Ctrl-C pressed, exiting ...")
         log.info("")
-        exit(0)
+        exit(1)
     except Exception as e:
         # Check if it's a certain kind of `AttributeError` and give a hint in
         # that case.