Make sure git gc runs if needed when syncing git mirrors in cache dir to avoid them getting very stale

src/Composer/Util/Git.php

@@ -261,7 +261,7 @@ class Git
                 $commandCallable = function ($url) {
                     $sanitizedUrl = preg_replace('{://([^@]+?):(.+?)@}', '://', $url);
 
-                    return sprintf('git remote set-url origin %s && git remote update --prune origin && git remote set-url origin %s', ProcessExecutor::escape($url), ProcessExecutor::escape($sanitizedUrl));
+                    return sprintf('git remote set-url origin %s && git remote update --prune origin && git remote set-url origin %s && git gc --auto', ProcessExecutor::escape($url), ProcessExecutor::escape($sanitizedUrl));
                 };
                 $this->runCommand($commandCallable, $url, $dir);
             } catch (\Exception $e) {