CI: Amend 943fd21.

.github/workflows/build.yml

@@ -324,7 +324,7 @@ jobs:
         EOF
         g++ -I. -std=c++11 -Wall -Wformat -o example_single_file example_single_file.cpp
 
-    - name: Build example_null (with C++26)
+    - name: Build example_null (with C++20)
       run: |
         cat > example_single_file.cpp <<'EOF'
 
@@ -334,7 +334,7 @@ jobs:
         #include "examples/example_null/main.cpp"
 
         EOF
-        g++ -I. -std=c++26 -Wall -Wformat -o example_single_file example_single_file.cpp
+        g++ -I. -std=c++20 -Wall -Wformat -o example_single_file example_single_file.cpp
 
     - name: Build example_null (with IMGUI_DISABLE_DEMO_WINDOWS and IMGUI_DISABLE_DEBUG_TOOLS)
       run: |