hydraJobs.tests.notifications: fixup file reference

Dependencies

• [2] 2JJP7673 tests: move to t, allow `yath test` from root
• [3] Z3JVFE2R Convert all tests to the Python DSL
• [4] RWNXH3H2 lastModified -> lastModifiedDate

Change contents

• replacement in flake.nix at line 557
  [3.1882]→[2.497:566](∅→∅)
  − cp ${./t/api-test.nix} /run/jobset/default.nix
  [3.1882]

  [3.1955]
  + cp ${./t/jobs/api-test.nix} /run/jobset/default.nix