fix: install FFmpeg dev packages for CNA's video-decoding pkg-config check

Configure now gets past SDL3's X11/XTEST checks and the easy-gl sibling
checkout (previous 3 commits), and fails one step further: CNA's
CMakeLists.txt unconditionally (on any non-MinGW/Emscripten/Android
build) does `pkg_check_modules(... REQUIRED libavcodec/libavformat/
libavutil/libswresample)` for its FFmpeg-based video decoding, and
none of those 4 pkg-config modules were installed.

Added libavcodec-dev, libavformat-dev, libavutil-dev,
libswresample-dev to both editor jobs' apt-get install lists.

Author: robertvokac

.github/workflows/ci.yml

@@ -287,6 +287,7 @@ jobs:
             libvulkan-dev \
             libx11-dev libxext-dev libxrandr-dev libxcursor-dev \
             libxi-dev libxfixes-dev libxss-dev libxtst-dev \
+            libavcodec-dev libavformat-dev libavutil-dev libswresample-dev \
             libsqlite3-dev libssl-dev libxml2-dev xvfb x11-utils
 
       - name: Cache root CMake FetchContent downloads
@@ -386,6 +387,7 @@ jobs:
             libgl1-mesa-dev libegl1-mesa-dev libglvnd-dev \
             libx11-dev libxext-dev libxrandr-dev libxcursor-dev \
             libxi-dev libxfixes-dev libxss-dev libxtst-dev \
+            libavcodec-dev libavformat-dev libavutil-dev libswresample-dev \
             libsqlite3-dev libssl-dev libxml2-dev xvfb x11-utils
 
       - name: Cache root CMake FetchContent downloads