feat: updating twitter to x (formerly twitter) (#125)

This PR is to suggest changing the Twitter text at in the footer to be
"X (formerly Twitter)" so that we stay current with naming/branding.

This is in response to discussion being had during the [January 11
Advocacy & Outreach
meeting](https://community.jenkins.io/t/advocacy-outreach-sig-meeting-2024-01-11/11739)

Several other projects are still using _just_ Twitter, but the CD
Foundation is using the X logo, so we want to try and align with them as
best we can.

If there are any thoughts or feelings against this idea, it would be
great to see other examples of how this is being addressed.

src/jio-footer.ts

@@ -151,7 +151,7 @@ export class Footer extends LitElement {
                               <a href=${relOrAbsoluteLink('/sigs/', this.property).href}>${msg('Special Interest Groups')}</a>
                            </li>
                            <li>
-                              <a href=${relOrAbsoluteLink('https://twitter.com/jenkinsci', this.property).href}>${msg('Twitter')}</a>
+                              <a href=${relOrAbsoluteLink('https://twitter.com/jenkinsci', this.property).href}>${msg('𝕏 (formerly Twitter)')}</a>
                            </li>
                            <li>
                               <a href=${relOrAbsoluteLink('https://reddit.com/r/jenkinsci', this.property).href}>${msg('Reddit')}</a>