ci: use stable toolchain to run clippy

.github/workflows/merge.yaml

@@ -8,48 +8,33 @@ name: Merge checks
 
 jobs:
   check:
-    name: Check
+    name: Checks
     runs-on: ubuntu-latest
     steps:
       - name: Checkout sources
         uses: actions/checkout@v4
 
       - name: Install rust toolchain
         uses: dtolnay/[email protected]
+        with:
+          components: clippy
 
       - name: Run cargo check
         run: cargo check --features sixel
 
-  test:
-    name: Tests
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout sources
-        uses: actions/checkout@v4
-
-      - name: Install rust toolchain
-        uses: dtolnay/[email protected]
-
       - name: Run cargo test
         run: cargo test
 
-  lints:
-    name: Lints
-    runs-on: ubuntu-latest
-    steps:
-      - name: Checkout sources
-        uses: actions/checkout@v4
+      - name: Run cargo clippy
+        run: cargo clippy -- -D warnings
 
-      - name: Install stable toolchain
+      - name: Install nightly toolchain
         uses: dtolnay/rust-toolchain@nightly
         with:
-          components: rustfmt, clippy
+          components: rustfmt
 
       - name: Run cargo fmt
-        run: cargo fmt --all -- --check
-
-      - name: Run cargo clippy
-        run: cargo clippy -- -D warnings
+        run: cargo +nightly fmt --all -- --check
 
   nix-flake:
     name: Validate nix flake