Revert to older emscripten: This 3.1.6 was just randomly picked, looking for an older version

Dockerfile-ubuntu2404

@@ -36,12 +36,13 @@ RUN apt-get update && \
 RUN sudo apt-get update && \
     sudo apt-get install -y cmake
 
-# Install emscripten deps
+# Install emscripten deps (EDIT: was using default branch, and 'latest' instead of 3.1.6, but I think something broke recently w/r/t keyboard handling)
 RUN sudo apt-get install -y libsdl2-dev && \
     (git clone https://github.com/emscripten-core/emsdk.git || true) && \
     cd emsdk && \
-    ./emsdk install latest && \
-    ./emsdk activate latest && \
+    git checkout 3.1.6 && \
+    ./emsdk install 3.1.6 && \
+    ./emsdk activate 3.1.6 && \
     sudo cp -prv ./emsdk_env.sh /etc/profile.d/
 
 # Warmup emscripten (this will pre-fetch SDL2, and cache it)