Update team membership requirement for /ok-to-test execution (#6732)

# Description

Update `/ok-to-test` command so it can only be triggered by
approvers-radius.

## Type of change

- This pull request fixes a bug in Radius and has an approved issue
(issue link required).

Fixes: #6715

## Auto-generated summary

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### <samp>🤖 Generated by Copilot at f836107</samp>

### Summary
:recycle::busts_in_silhouette::wrench:

<!--
1. :recycle: - This emoji can be used to indicate a refactor or update
of existing code or configuration, without changing the functionality or
behavior. In this case, the environment variable is updated to reflect
the new team name, but the workflow logic remains the same.
2. :busts_in_silhouette: - This emoji can be used to indicate a change
related to users, groups, teams, or roles. In this case, the team
`approvers-radius` is a new group of users who are responsible for
reviewing and approving pull requests for the radius project.
3. :wrench: - This emoji can be used to indicate a change related to
tools, settings, or configuration. In this case, the environment
variable is a setting that controls how the radius-bot workflow operates
and interacts with GitHub.
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Updated the radius-bot workflow to use the new `approvers-radius` team
for pull request approvals. This team includes the core maintainers and
reviewers of the radius project.

> _`TEAM_SLUG` changes_
> _New team structure for radius_
> _Autumn of refactor_

### Walkthrough
* Update the team name for approving pull requests in the radius-bot
workflow
([link](https://github.com/radius-project/radius/pull/6732/files?diff=unified&w=0#diff-c70ecfd035a4650c141a6b69858c30ad9a9f261099f3c891b6bd44f7021ba9ceL21-R21))

Signed-off-by: Karishma Chawla <[email protected]>

.github/workflows/radius-bot.yaml

@@ -18,7 +18,7 @@ jobs:
       - name: Comment analyzer
         uses: actions/github-script@v6
         env:
-          TEAM_SLUG: 'Radius-Eng'
+          TEAM_SLUG: 'approvers-radius'
         with:
           github-token: ${{ secrets.GH_RAD_CI_BOT_PAT }}
           script: |