infra: Put SDL2 headless release inside a GUI-less block in PR (#3218)

As title say.

.github/workflows/nightly_pr_comment.yml

@@ -36,15 +36,20 @@ jobs:
               return core.error(`No artifacts found`);
             }
             let body = `Download the artifacts for this pull request:\n`;
+            let hidden_headless_artifacts = `\n\n <details><summary>GUI-less (SDL2)</summary>\n`;
             let hidden_debug_artifacts = `\n\n <details><summary>Only for Developers</summary>\n`;
             for (const art of artifacts) {
-              if(art.name.includes('Debug')){
+              if(art.name.includes('Debug')) {
                 hidden_debug_artifacts += `\n* [${art.name}](https://nightly.link/${owner}/${repo}/actions/artifacts/${art.id}.zip)`;
-              }else{
+              } else if(art.name.includes('headless-sdl2')) {
+                hidden_headless_artifacts += `\n* [${art.name}](https://nightly.link/${owner}/${repo}/actions/artifacts/${art.id}.zip)`;
+              } else {
                 body += `\n* [${art.name}](https://nightly.link/${owner}/${repo}/actions/artifacts/${art.id}.zip)`;
               }
             }
+            hidden_headless_artifacts += `\n</details>`;
             hidden_debug_artifacts += `\n</details>`;
+            body += hidden_headless_artifacts;
             body += hidden_debug_artifacts;
 
             const {data: comments} = await github.issues.listComments({repo, owner, issue_number});