Pin clang-format install

Co-authored-by: Cursor <cursoragent@cursor.com>

.github/workflows/lint.yml

@@ -19,9 +19,15 @@ jobs:
 
     - name: Install clang-format
       run: |
-        wget https://apt.llvm.org/llvm.sh
-        sudo bash ./llvm.sh 21
-        sudo apt install clang-format-21
+        sudo install -D -m 0644 support/llvm-snapshot.gpg.key \
+          /etc/apt/keyrings/apt.llvm.org.asc
+        codename=$(lsb_release -cs)
+        echo "deb [signed-by=/etc/apt/keyrings/apt.llvm.org.asc]" \
+             "https://apt.llvm.org/$codename/" \
+             "llvm-toolchain-$codename-21 main" \
+          | sudo tee /etc/apt/sources.list.d/llvm.list
+        sudo apt-get update
+        sudo apt-get install -y clang-format-21
 
     - name: Run clang-format
       run: |