[docs] Fix code edit for when v6 will be stable (#6600)

docs/pages/_app.js

@@ -30,7 +30,7 @@ LicenseInfo.setLicenseKey(process.env.NEXT_PUBLIC_MUI_LICENSE);
 
 function getMuiPackageVersion(packageName, commitRef) {
   if (commitRef === undefined) {
-    return 'latest';
+    return '^5.0.0';
   }
   const shortSha = commitRef.slice(0, 8);
   return `https://pkg.csb.dev/mui/mui-x/commit/${shortSha}/@mui/${packageName}`;