CI: test with ImTextureID as pointer to catch accidental reuse of const (#4060)

.github/workflows/build.yml

@@ -254,10 +254,11 @@ jobs:
         EOF
         g++ -I. -Wall -Wformat -o example_single_file example_single_file.cpp
 
-    - name: Build example_null (with large ImDrawIdx)
+    - name: Build example_null (with large ImDrawIdx + pointer ImTextureID)
       run: |
         cat > example_single_file.cpp <<'EOF'
 
+        #define ImTextureID void*
         #define ImDrawIdx unsigned int
         #define IMGUI_IMPLEMENTATION
         #include "misc/single_file/imgui_single_file.h"