ci: fix Fedora mingw OpenCV include path

CMakeLists.txt

@@ -15,6 +15,17 @@ endif()
 
 find_package(OpenCV REQUIRED COMPONENTS core imgproc imgcodecs)
 
+# Fedora MinGW OpenCV 4.13.0 may report an invalid include directory
+# (//include/opencv4) from its OpenCVConfig.cmake. The headers are in the
+# MinGW sysroot, so add a narrow cross-build fallback when CMake did not get a
+# usable OpenCV include path from the package config.
+if (MINGW AND (NOT OpenCV_INCLUDE_DIRS OR NOT EXISTS "${OpenCV_INCLUDE_DIRS}"))
+    set(_fedora_mingw_opencv_include "/usr/x86_64-w64-mingw32/sys-root/mingw/include/opencv4")
+    if (EXISTS "${_fedora_mingw_opencv_include}")
+        set(OpenCV_INCLUDE_DIRS "${_fedora_mingw_opencv_include}")
+    endif()
+endif()
+
 set(PROJECT_SOURCES
     app/src/main.cpp
     app/src/MainWindow.cpp