[ci] fix fmt require rust nightly image

.gitlab-ci.yml

@@ -15,12 +15,20 @@ variables:
     - export PATH="$HOME/.cargo/bin:$PATH"
     - rustc --version && cargo --version
 
+.rust_nightly_lin64: &rust_nightly_lin64
+  image: rustlang/rust:nightly
+  tags:
+    - redshift-rs-nightly
+  before_script:
+    - export PATH="$HOME/.cargo/bin:$PATH"
+    - rustc --version && cargo --version
+
 fmt:
-  <<: *rust_stable_wasm
+  <<: *rust_nightly_lin64
   stage: fmt
   before_script:
     - rustup show
-    - rustup component add rustfmt-preview
+    - rustup component add rustfmt-preview --toolchain nightly
     - cargo fmt -- --version
   script:
     - cargo fmt -- --check