Fix: s/pushd/cd

Dockerfile-ubuntu2004

@@ -35,7 +35,7 @@ RUN wget https://github.com/Kitware/CMake/releases/download/v3.21.3/cmake-3.21.3
 RUN sudo apt-get update && \
     sudo apt-get install -y libsdl2-dev && \
     (git clone https://github.com/emscripten-core/emsdk.git || true) && \
-    pushd emsdk && \
+    cd emsdk && \
     ./emsdk install latest && \
     ./emsdk activate latest && \
     sudo cp -prv ./emsdk_env.sh /etc/profile.d/