Backport nightly toolchain due to assumed miri regression

Author: zetanumbers

.github/workflows/push-check.yml

@@ -25,7 +25,7 @@ jobs:
         with:
           fetch-depth: 0
       - name: Install Rust toolchain
-        uses: dtolnay/rust-toolchain@nightly
+        uses: dtolnay/rust-toolchain@nightly-2025-05-05
         with:
           components: miri
       - name: Stacked borrows

flake.lock

@@ -17,7 +17,7 @@
           pkgs = import nixpkgs {
             inherit system overlays;
           };
-          rustToolchain = pkgs.pkgsBuildHost.rust-bin.selectLatestNightlyWith (toolchain: toolchain.default.override {
+          rustToolchain = (pkgs.pkgsBuildHost.rust-bin.nightly."2025-05-05".default.override {
             extensions = [ "rust-src" "rust-analyzer" "miri" ];
           });
         in