Use git reset instead of git pull to avoid attempting a merge commit

Also, use git remote set-head in case the repository’s default branch
has been renamed.

Fixes yarnpkg#5303.

Signed-off-by: Anders Kaseorg <[email protected]>

Author: andersk

src/util/git.js

@@ -320,7 +320,8 @@ export default class Git implements GitRefResolvingInterface {
     return fs.lockQueue.push(gitUrl.repository, async () => {
       if (await fs.exists(cwd)) {
         await spawnGit(['fetch', '--tags'], {cwd});
-        await spawnGit(['pull'], {cwd});
+        await spawnGit(['remote', 'set-head', 'origin', '--auto'], {cwd});
+        await spawnGit(['reset', '--hard', 'origin/HEAD'], {cwd});
       } else {
         await spawnGit(['clone', gitUrl.repository, cwd]);
       }