Fetch the rustc-dep-of-std branch before rebasing over it.

Author: sunfishcode

.github/workflows/test-users.yml

@@ -345,6 +345,7 @@ jobs:
         # Fetch enough to let the bootstrap script find an LLVM revision.
         fetch-depth: 2000
     # Include the changes needed to support std.
+    - run: git fetch --depth=1 origin rustc-dep-of-std
     - run: git rebase rustc-dep-of-std
     # Download a pre-built LLVM instead of building it from source.
     - run: cd rust && echo "[llvm]" >> config.toml