ci: fix creating issue comment (#1433)

Author: madsmtm

.github/workflows/test-rustc-targets.yml

@@ -42,13 +42,11 @@ jobs:
           GH_TOKEN: ${{ secrets.GITHUB_TOKEN }}
         run: |
           gh issue comment 1426 --body "
-          Failed parsing `rustc` target on `$(rustc --version)`.
+          Failed parsing \`rustc\` target on \`$(rustc --version)\`.
+
+          Test output:
 
-          <details><summary>Test output</summary>
-          <p>
           \`\`\`
           $(cat test_output.txt)
           \`\`\`
-          </p>
-          </details>
-          " --head $(git branch --show-current)
+          "