[BUG] Replace repo_token with github_token in Auto Assign PR GHA

[Matt711]

Description

The Auto Assign GHA workflow fails with this error. This PR fixes this error.
xref #16969

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

[Matt711]

CI is currently fails with this error:

Warning: Unexpected input(s) 'repo_token', valid inputs are ['github_token', 'assignees', 'repo', 'number']
Run actions-ecosystem/action-add-assignees@v1
Error: Error: Input required and not supplied: github_token
Error: Input required and not supplied: github_token

This is the error that this PR will fix, so it may have to be merged as it is.

[Matt711]

/merge