imports: sort imports everywhere in Spack (#24695)

* fix remaining flake8 errors

* imports: sort imports everywhere in Spack

We enabled import order checking in #23947, but fixing things manually drives
people crazy. This used `spack style --fix --all` from #24071 to automatically
sort everything in Spack so PR submitters won't have to deal with it.

This should go in after #24071, as it assumes we're using `isort`, not
`flake8-import-order` to order things. `isort` seems to be more flexible and
allows `llnl` mports to be in their own group before `spack` ones, so this
seems like a good switch.

.github/workflows/unit_tests.yaml

@@ -370,7 +370,7 @@ jobs:
       run: |
           pip install --upgrade pip six setuptools
           pip install --upgrade codecov coverage
-          pip install --upgrade flake8 isort>=4.3.5 pep8-naming mypy>=0.800
+          pip install --upgrade flake8 isort>=4.3.5 mypy>=0.800
     - name: Setup Homebrew packages
       run: |
         brew install dash fish gcc gnupg2 kcov