feat(pay-page): conditionally style referral avatar images

Add a conditional check on avatarIsGitHubAvatar to apply a border and 
rounded styling to GitHub avatars for better visual consistency. Non-
GitHub avatars retain the original styling. This improves the UI by 
differentiating avatar types and enhancing the referral discount 
notice's
appearance.

Author: rohitpaulk

app/components/pay-page/referral-discount-notice.hbs

@@ -8,11 +8,15 @@
   </div>
 
   <div class="bg-repeating-gradient-to-b from-yellow-100 to-amber-500 text-transparent bg-clip-text leading-7 inline-block mt-0.5">
-    <img
-      alt="avatar"
-      src={{@discount.affiliateReferral.affiliateLink.affiliateAvatarUrl}}
-      class="inline-block mb-0 w-6 h-6 transform -translate-y-px"
-    />
+    {{#if @discount.affiliateReferral.affiliateLink.avatarIsGitHubAvatar}}
+      <img
+        alt="avatar"
+        src={{@discount.affiliateReferral.affiliateLink.affiliateAvatarUrl}}
+        class="inline-block w-6 h-6 border border-gray-100 rounded-full transform -translate-y-px"
+      />
+    {{else}}
+      <img alt="avatar" src={{@discount.affiliateReferral.affiliateLink.affiliateAvatarUrl}} class="inline-block w-6 h-6" />
+    {{/if}}
 
     <b>{{@discount.affiliateReferral.affiliateLink.affiliateUsername}}</b>'s referral offer: Subscribe in
     <span class="font-bold percy-timestamp font-mono text-lg border-b border-yellow-500 border-dashed">{{this.timeLeftText}}</span>