fix: retry prune operations

This is involves the server, so it fails when server is unavailable

autogitmerge.mjs

@@ -27,8 +27,8 @@ if (!fs.existsSync(wd)) {
 cd(wd)
 let reportedConflictHashes
 while (true) {
-  await $`git remote prune project`
-  await $`git remote prune upstream`
+  await retry(30, expBackoff(), () => $`git remote prune project`)
+  await retry(30, expBackoff(), () => $`git remote prune upstream`)
   await retry(30, expBackoff(), () => $`git fetch --all`)
 
   await $`git reset --hard project/${config.project.branch}`