Add rustc commit hash to rust-toolchain.toml for UI tests

Author: cds-amal

rust-toolchain.toml

@@ -1,3 +1,10 @@
 [toolchain]
 channel = "nightly-2024-11-29"
 components = ["llvm-tools", "rustc-dev", "rust-src", "rust-analyzer"]
+
+# Ignored by rustup; used by our test scripts.
+# This is the rustc commit that backs the nightly above.
+# UI tests (make test-ui, make remake-ui-tests) need a rust compiler
+# checkout at this commit: git -C $RUST_DIR_ROOT checkout <commit>
+[metadata]
+rustc-commit = "a2545fd6fc66b4323f555223a860c451885d1d2b"