ci: Factorize CI conda environment

Author: jorisv

.github/workflows/ci-windows.yml

@@ -30,16 +30,10 @@ jobs:
       with:
         activate-environment: pycppad
         auto-update-conda: true
-        environment-file: .github/workflows/conda/conda-env-win.yml
+        environment-file: .github/workflows/conda/conda-env.yml
         python-version: 3.8
         auto-activate-base: false
 
-    - name: Setup cppad codegen
-      if: contains(matrix.compiler.cmd, 'clang')
-      shell: cmd /C CALL {0}
-      run: |
-        conda install cppadcodegen
-
     - name: Build PyCppAD
       shell: cmd /C CALL {0}
       run: |