Move nightly CI tests to the main branch

Fuzz tests set up with cron don't run because cron scheduled workflows
are triggered only for the default branch.
Add nightly workflow file to the default branch with fuzz tests
specified to run on 'adapters' branch.

.github/workflows/nightly.yml

@@ -0,0 +1,53 @@
+name: Nightly
+
+on:
+  schedule:
+    # Run every day at 23:00 UTC
+    - cron: '0 23 * * *'
+
+jobs:
+  long-fuzz-test:
+    name: Run long fuzz tests
+    strategy:
+      matrix:
+        build_type: [Debug, Release]
+        compiler: [{c: clang, cxx: clang++}]
+
+    runs-on: 'ubuntu-22.04'
+
+    steps:
+    - uses: actions/checkout@v3
+      # with-ref part to be removed after merging 'adapters' branch with 'main'
+      with:
+        ref: adapters
+
+    - name: Install pip packages
+      run: pip install -r third_party/requirements.txt
+
+    - name: Download DPC++
+      run: |
+        wget -O ${{github.workspace}}/dpcpp_compiler.tar.gz https://github.com/intel/llvm/releases/download/nightly-2023-08-31/sycl_linux.tar.gz
+        mkdir dpcpp_compiler
+        tar -xvf ${{github.workspace}}/dpcpp_compiler.tar.gz -C dpcpp_compiler
+
+    - name: Configure CMake
+      run: >
+        cmake
+        -B${{github.workspace}}/build
+        -DCMAKE_C_COMPILER=${{matrix.compiler.c}}
+        -DCMAKE_CXX_COMPILER=${{matrix.compiler.cxx}}
+        -DUR_ENABLE_TRACING=ON
+        -DCMAKE_BUILD_TYPE=${{matrix.build_type}}
+        -DUR_BUILD_TESTS=ON
+        -DUR_USE_ASAN=ON
+        -DUR_USE_UBSAN=ON
+        -DUR_DPCXX=${{github.workspace}}/dpcpp_compiler/bin/clang++
+
+    - name: Build
+      run: >
+        LD_LIBRARY_PATH=${{github.workspace}}/dpcpp_compiler/lib
+        cmake --build ${{github.workspace}}/build -j $(nproc)
+
+    - name: Fuzz long test
+      working-directory: ${{github.workspace}}/build
+      run: ctest -C ${{matrix.build_type}} --output-on-failure -L "fuzz-long"