chore(repo): fix assignment rules to prevent early termination (#30382)

<!-- Please make sure you have read the submission guidelines before
posting an PR -->
<!--
https://github.com/nrwl/nx/blob/master/CONTRIBUTING.md#-submitting-a-pr
-->

<!-- Please make sure that your commit message follows our format -->
<!-- Example: `fix(nx): must begin with lowercase` -->

<!-- If this is a particularly complex change or feature addition, you
can request a dedicated Nx release for this pull request branch. Mention
someone from the Nx team or the `@nrwl/nx-pipelines-reviewers` and they
will confirm if the PR warrants its own release for testing purposes,
and generate it for you if appropriate. -->

## Current Behavior
<!-- This is the behavior we have today --> 

We set assignment rules to default all tasks to medium, which meant that
after the `linux-large` agent was complete, it would terminate since no
tasks would be assigned to it. This fixes the rules to ensure that tasks
can also be assigned to the linux-large agent.

## Expected Behavior
<!-- This is the behavior we should expect with the changes in this PR
-->

## Related Issue(s)
<!-- Please link the issue being fixed so it gets closed when this is
merged. -->

Fixes #

.nx/workflows/dynamic-changesets.yaml

@@ -20,3 +20,5 @@ assignment-rules:
     run-on:
       - agent: linux-medium
         parallelism: 3
+      - agent: linux-extra-large
+        parallelism: 3