pin emscripten on ci

this might call for another composite...
second attempt at pinning emscripten

Author: PgBiel

.github/workflows/minimal-ci.yml

@@ -143,11 +143,14 @@ jobs:
           rust: nightly
 
       - name: "Install emscripten"
+        env:
+          EMSCRIPTEN_SRC_REF: 4.0.13
+          EMSCRIPTEN_VERSION: 3.1.74
         run: |
-          git clone https://github.com/emscripten-core/emsdk.git
+          git clone https://github.com/emscripten-core/emsdk.git --depth 1 --branch $EMSCRIPTEN_SRC_REF --single-branch
           pushd emsdk
-          ./emsdk install 3.1.74
-          ./emsdk activate 3.1.74
+          ./emsdk install $EMSCRIPTEN_VERSION 
+          ./emsdk activate $EMSCRIPTEN_VERSION
           source ./emsdk_env.sh
           popd