"indexed documents" count is not being updated when count changes

[stovak]

Describe the bug
The number of indexed documents is not being updated when the number changes. Drupal's form caching is preventing the changed number from updating.

To Reproduce
Steps to reproduce the behavior:

1. Go to '/admin/config/search/search-api/server/pantheon_solr8'
2. Observe the indexed document count. If it has changed in the same user session, the count will be incorrect.

Expected behavior
The indexed count should always update with every page view