Prevented linking to GitHub for pre-releases

- if we're running a pre-release, we haven't released it on GitHub so
  Admin shouldn't provide a link to it
- instead of pulling in `semver`, I've just gone for the simpler method
  of looking for the pre-release string identifier

ghost/admin/app/controllers/whatsnew.js

@@ -13,6 +13,12 @@ export default class WhatsNewController extends Controller {
         return date.getFullYear();
     }
 
+    get linkToGitHubReleases() {
+        // Don't link to GitHub Releases if the version contains the
+        // pre-release identifier
+        return !this.config.get('version').includes('-pre.');
+    }
+
     get showSystemInfo() {
         const isPro = !!this.config.get('hostSettings')?.siteId;
 

ghost/admin/app/templates/whatsnew.hbs

@@ -50,7 +50,11 @@
                 {{/if}}
 
                 <ul class="gh-env-list">
+                    {{#if this.linkToGitHubReleases}}
                     <li><strong>Version:</strong> <a href="https://github.com/TryGhost/Ghost/releases/tag/v{{this.config.version}}" target="_blank" rel="noopener noreferrer">{{this.config.version}}</a></li>
+                    {{else}}
+                    <li><strong>Version:</strong> {{this.config.version}}</li>
+                    {{/if}}
                     {{#if this.showSystemInfo}}
                     <li><strong>Environment:</strong> <span class="ttc">{{this.config.environment}}</span></li>
                     <li class="gh-env-list-database-type"><strong>Database:</strong> {{this.config.database}}</li>