CI: remove prebuilt toolchains

.github/workflows/unit.yml

@@ -2,15 +2,14 @@ name: Unit tests
 
 on:
   push:
-    branches: [ "main" ]
+    branches: ["main"]
   pull_request:
-    branches: [ "main" ]
+    branches: ["main"]
 
 env:
   # Customize the CMake build type here (Release, Debug, RelWithDebInfo, etc.)
   BUILD_TYPE: Debug
   TEST_MODE: UNIT
-  BUILD_PARALLEL: 3
 
 jobs:
   build:
@@ -35,7 +34,7 @@ jobs:
 
       - name: Build
         # Build your program with the given configuration
-        run: cmake --build ${{github.workspace}}/build --config ${{env.BUILD_TYPE}}  --parallel ${{env.BUILD_PARALLEL}}
+        run: cmake --build ${{github.workspace}}/build --config ${{env.BUILD_TYPE}}  --parallel $(nproc)
 
       - name: Test
         # Execute tests defined by the CMake configuration.