Fix CI.yml

Author: ufechner7

.github/workflows/CI.yml

@@ -79,9 +79,6 @@ jobs:
           - ubuntu-latest
     runs-on: ${{ matrix.os }}
     steps:
-    - name: Build PyCall
-      run: julia --project -e 'ENV["PYTHON"]=""; using Pkg; Pkg.instantiate(); Pkg.add("PyCall"); Pkg.build("PyCall")'
-      shell: bash
     - name: Install matplotlib
       run: if [ "$RUNNER_OS" = "Linux" ]; then sudo apt-get install -y python3-matplotlib; fi
       shell: bash
@@ -90,10 +87,11 @@ jobs:
       with:
         arch: ${{ matrix.julia_arch }}
         version: ${{ matrix.julia_version }}
+    - uses: julia-actions/cache@v2
+    - uses: julia-actions/julia-buildpkg@v1
     - name: Build PyCall
       run: julia --project -e 'ENV["PYTHON"]=""; using Pkg; Pkg.instantiate(); Pkg.add("PyCall"); Pkg.build("PyCall")'
       shell: bash    
-    - uses: julia-actions/cache@v2
     - uses: julia-actions/julia-runtest@v1
       env:
         BUILD_IS_PRODUCTION_BUILD: false