Append query parameter to downloads

This allows mirrors to know how much traffic is coming from Actions, and
hence allows us to observe if some mirrors are having bandwidth or usage
issues due to this Action. The query parameter is hardcoded as
`?source=github-actions`, and contains no information about the
workflow, job, or run.

Author: mlugg

main.js

@@ -21,9 +21,9 @@ const MIRRORS = [
 ];
 
 async function downloadFromMirror(mirror, tarball_name, tarball_ext) {
-  const tarball_path = await tc.downloadTool(`${mirror}/${tarball_name}${tarball_ext}`);
+  const tarball_path = await tc.downloadTool(`${mirror}/${tarball_name}${tarball_ext}?source=github-actions`);
 
-  const signature_response = await fetch(`${mirror}/${tarball_name}${tarball_ext}.minisig`);
+  const signature_response = await fetch(`${mirror}/${tarball_name}${tarball_ext}.minisig?source=github-actions`);
   const signature_data = Buffer.from(await signature_response.arrayBuffer());
 
   const tarball_data = await fs.readFile(tarball_path);