Use nightly toolchain for rustfmt CI

Author: Bromeon

.github/workflows/full-ci.yml

@@ -49,6 +49,7 @@ jobs:
       - name: "Install Rust"
         uses: ./.github/composite/rust
         with:
+          rust: nightly
           components: rustfmt
 
       - name: "Check rustfmt"

.github/workflows/minimal-ci.yml

@@ -47,6 +47,7 @@ jobs:
       - name: "Install Rust"
         uses: ./.github/composite/rust
         with:
+          rust: nightly
           components: rustfmt
 
       - name: "Check rustfmt"

.github/workflows/release-version.yml

@@ -120,7 +120,7 @@ jobs:
           ref: ${{ github.ref }}
 
       - name: "Install Rust (uncached)"
-        run: rustup update stable
+        run: rustup update nightly && rustup default nightly
 
       - name: "Check rustfmt"
         run: cargo fmt --all -- --check