Fix AttributeError in index_registry task

[alikins]

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What is this PR doing:

The task was previously attempting to use a ValidationError from a 'serializers' import that didn't define it.

Use the rest_framework.exceptions.ValidationError instead.

Issue: AAH-1966

Reviewers must know:

To reproduce:

1. Bring a standalone env (./compose up)
2. run integration tests ( HUB_LOCAL=1 ./dev/common/RUN_INTEGRATION.sh)
3. watch/grep the logs for above traceback (there should be some before the fix, but none after)

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[jctanner]

This looks like it can be unit tested.

[patchback[bot]]

Backport to stable-4.2: 💔 cherry-picking failed — conflicts found

❌ Failed to cleanly apply b8d860b03b97d7448860c2e5ff6c7674f840cdb5 on top of patchback/backports/stable-4.2/b8d860b03b97d7448860c2e5ff6c7674f840cdb5/pr-1521

Backporting merged PR #1521 into master

1. Ensure you have a local repo clone of your fork. Unless you cloned it from the upstream, this would be your origin remote.
2. Make sure you have an upstream repo added as a remote too. In these instructions you'll refer to it by the name upstream. If you don't have it, here's how you can add it:

   $ git remote add upstream https://github.com/ansible/galaxy_ng.git
   

3. Ensure you have the latest copy of upstream and prepare a branch that will hold the backported code:

   $ git fetch upstream
   $ git checkout -b patchback/backports/stable-4.2/b8d860b03b97d7448860c2e5ff6c7674f840cdb5/pr-1521 upstream/stable-4.2
   

4. Now, cherry-pick PR #1521 contents into that branch:

   $ git cherry-pick -x b8d860b03b97d7448860c2e5ff6c7674f840cdb5
   

   If it'll yell at you with something like fatal: Commit b8d860b03b97d7448860c2e5ff6c7674f840cdb5 is a merge but no -m option was given., add -m 1 as follows intead:

   $ git cherry-pick -m1 -x b8d860b03b97d7448860c2e5ff6c7674f840cdb5
   

5. At this point, you'll probably encounter some merge conflicts. You must resolve them in to preserve the patch from PR #1521 as close to the original as possible.
6. Push this branch to your fork on GitHub:

   $ git push origin patchback/backports/stable-4.2/b8d860b03b97d7448860c2e5ff6c7674f840cdb5/pr-1521
   

7. Create a PR, ensure that the CI is green. If it's not — update it so that the tests and any other checks pass. This is it! Now relax and wait for the maintainers to process your pull request when they have some cycles to do reviews. Don't worry — they'll tell you if any improvements are necessary when the time comes!

🤖 @patchback I'm built with octomachinery and my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback[bot]]

Backport to stable-4.4: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-4.4/b8d860b03b97d7448860c2e5ff6c7674f840cdb5/pr-1521

Backported as https://github.com/ansible/galaxy_ng/pull/1537

🤖 @patchback I'm built with octomachinery and my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback[bot]]

Backport to stable-4.5: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-4.5/b8d860b03b97d7448860c2e5ff6c7674f840cdb5/pr-1521

Backported as https://github.com/ansible/galaxy_ng/pull/1538

🤖 @patchback I'm built with octomachinery and my source is open — https://github.com/sanitizers/patchback-github-app.

[patchback[bot]]

Backport to stable-4.6: 💚 backport PR created

✅ Backport PR branch: patchback/backports/stable-4.6/b8d860b03b97d7448860c2e5ff6c7674f840cdb5/pr-1521

Backported as https://github.com/ansible/galaxy_ng/pull/1539

🤖 @patchback I'm built with octomachinery and my source is open — https://github.com/sanitizers/patchback-github-app.