[EN-1228] generate docs only once

Author: iamishalkin

.github/workflow/pythonpackage.yml

@@ -77,4 +77,4 @@ jobs:
       run: |
         task html_docs
       shell: bash
-      if: matrix.os == 'ubuntu-latest'
+      if: matrix.os == 'ubuntu-latest' && matrix.python-version == 3.7