Fixes CNCF footer link

Signed-off-by: Esteban Torres <me+github@estebantorr.es>

@jenjamall noticed on #10376 that the footer
linking to `CNCF` projects was outdated and
pointing to `sandbox` projects instead of the ones
in incubation and graduated.

microsite/core/Footer.js

@@ -51,7 +51,7 @@ class Footer extends React.Component {
             <a href="https://mailchi.mp/spotify/backstage-community">
               Subscribe to our newsletter
             </a>
-            <a href="https://www.cncf.io/sandbox-projects/">CNCF Incubation</a>
+            <a href="https://www.cncf.io/projects/">CNCF Incubation</a>
           </div>
           <div>
             <h5>More</h5>