fix conda build

Signed-off-by: Martijn Govers <Martijn.Govers@Alliander.com>

.github/workflows/main.yml

@@ -220,10 +220,10 @@ jobs:
     name: Build and test in Conda
     if: (github.event_name == 'push')  || (github.event_name == 'workflow_dispatch') || (!startsWith(github.head_ref, 'release'))
 
-    runs-on: ${{ matrix.os }}-latest
+    runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        os: ["ubuntu", "macos", "windows"]
+        os: ["ubuntu-latest", "macos-13", "windows-latest"]
 
     defaults:
       run:
@@ -241,6 +241,12 @@ jobs:
         run: |
           conda info
           conda list
+
+      - name: Set up XCode
+        if: matrix.os == 'macos-13'
+        uses: maxim-lobanov/setup-xcode@v1
+        with:
+          xcode-version: latest-stable
 
       - name: Build
         run: python -m pip install . -vv --no-build-isolation --no-deps