tests: Fix popup screen captures

Some popups like the keypad didn't get captured.

After debugging, I've narrowed it down to the
ImGuiCaptureFlags_StitchAll flag, which is about
capturing the whole scroll area content. Since the flag is unrelated
to popups, this seems like a bug in ImGuiTestEngine.

Signed-off-by: Sergio Martins <[email protected]>

src/ui/test/ImGuiTestApp.hpp

@@ -63,7 +63,7 @@ class ImGuiTestApp {
       @param ref An ImGuiID or a char* path that identifies the widget to be captured. Captures the window by default
       @param captureFlags See ImGui's ImGuiCaptureFlags_ enum
      */
-    static void captureScreenshot(ImGuiTestContext& ctx, ImGuiTestRef ref = "/", int captureFlags = ImGuiCaptureFlags_StitchAll | ImGuiCaptureFlags_HideMouseCursor | ImGuiCaptureFlags_IncludeTooltipsAndPopups | ImGuiCaptureFlags_IncludeOtherWindows);
+    static void captureScreenshot(ImGuiTestContext& ctx, ImGuiTestRef ref = "/", int captureFlags = ImGuiCaptureFlags_HideMouseCursor | ImGuiCaptureFlags_IncludeTooltipsAndPopups | ImGuiCaptureFlags_IncludeOtherWindows);
 
     // Prints the existing window ids, for debugging purposes
     static void printWindows();