use gcc:15 image for github

.github/workflows/verify.yml

@@ -1,4 +1,4 @@
-name: verify
+name: Backend
 
 on:
   push:
@@ -8,26 +8,17 @@ on:
 
 jobs:
   verify:
-    runs-on: ubuntu-latest
+    container: gcc:4.9
 
     steps:
     - uses: actions/checkout@v4
     - run: sudo apt-get install -y libmicrohttpd-dev
-    - name: install llvm
-      run: |
-        wget https://apt.llvm.org/llvm.sh
-        chmod +x llvm.sh
-        sudo ./llvm.sh 22 all
-    - name: versions
-      run: |
-        clang-22 --version
-        clang-format-22 --version
     - name: check
       working-directory: ./backend
-      run: make check CLANG_FORMAT=clang-format-22
+      run: make check
     - name: build
       working-directory: ./backend
-      run: make all LD=clang++-22 CXX=clang++-22
+      run: make all
     - name: test
       working-directory: ./backend
       run: make test