Improve output of `submodchecker`

It was confusing me a lot. Now it won't.

Now looks like:

Submodule update(s) detected in dac6686f4fddca4493a2b16e2dfa63a667d558ca:
 - libraries/Cabal => 23ca3cb318418aaf4aafd3db862278a12a794a26
 - libraries/array => 96cc02ad59179957251650b1078aa1a0723a4b18
   *FAIL* commit not found in submodule repo
          or not reachable from persistent branches

 - libraries/binary => 51ce49d67a67c12f8d530f6d50de243c9bab7c32
   *FAIL* commit not found in submodule repo
          or not reachable from persistent branches

 - libraries/bytestring => 75fd24e9a0b152ae32149a7b447456e647f00351
   *FAIL* commit not found in submodule repo
          or not reachable from persistent branches

 - libraries/containers => 34f5f4d4f4701437dc53e013965f72e59d616b70
   *FAIL* commit not found in submodule repo
          or not reachable from persistent branches

     Found the following non-mirred WIP branches:
      - wip/ghc-9.2-sized-array-primops -> 34f5f4d4f4701437dc53e013965f72e59d616b70

 - libraries/text => 3ed977de30e9fb74af33ce9ea4efa4a284c17bdb
   *FAIL* commit not found in submodule repo
          or not reachable from persistent branches

Changes are broken up into separate commits, if one is curious.