Bug: Slack invite link is inactive on Project List page

### Description
The Slack invitation link provided on the First Contributions project list page is no longer active. When clicked, it displays the following error:
> "This link is no longer active. To join this workspace, you’ll need to ask the person who originally invited you for a new link."

### Page URL
`https://firstcontributions.github.io/#project-list`

### Steps to Reproduce
1. Navigate to the First Contributions [Project List](https://firstcontributions.github.io/#project-list).
2. Locate the link to join the **Slack** community.
3. Click the link and observe the Slack error page.

### Expected Behavior
The link should provide a valid invite to the First Contributions Slack workspace.

### Suggested Fix
Update the invitation URL with a fresh, non-expiring link, or remove the Slack section if the workspace is no longer being actively maintained.