CI: pass full path to llvm-config

.github/workflows/build.yml

@@ -22,7 +22,7 @@ jobs:
         run: |
           sudo apt-get update
           sudo apt-get install -y clang-18 lld-18 llvm-18
-          echo "LLVM_CONFIG=llvm-config-18" >> "$GITHUB_ENV"
+          echo "LLVM_CONFIG=/usr/lib/llvm-18/bin/llvm-config" >> "$GITHUB_ENV"
 
       - name: Download SDKs
         env: