ci/conda: fix version parsing

Author: jcarpent

.github/workflows/macos-linux-conda.yml

@@ -24,7 +24,7 @@ jobs:
         activate-environment: eigenpy
         auto-update-conda: true
         environment-file: .github/workflows/conda/environment.yml
-        python-version: 3.10
+        python-version: '3.10'
 
     - uses: actions/cache@v2
       with: