apache-airflow: fix src.hash

Got broken due to limitations of the python bulk updater

pkgs/development/python-modules/apache-airflow/default.nix

···
     # Download using the git protocol rather than using tarballs, because the
     # GitHub archive tarballs don't appear to include tests
     forceFetchGit = true;
-    sha256 = "sha256-gE/kPFb5PyPOi6sqtA9YqMokbjVSKgclGNQ6fbiCdgQ=";
+    hash = "sha256-QWUXSG+RSHkF5kP1ZYtx+tHjO0n7hfya9CFA3lBhJHk=";
   };
 
   # airflow bundles a web interface, which is built using webpack by an undocumented shell script in airflow's source tree.