Added check to avoid running tests twice on non-fork PR. Removed unne…

…eded step. Changed mypy to run with latest py version used in tests

.github/workflows/main.yml

@@ -5,6 +5,7 @@ on: [push, pull_request]
 jobs:
   tests:
     runs-on: ubuntu-latest
+    if: github.event_name != 'pull_request' || github.event.pull_request.head.repo.full_name != github.event.pull_request.base.repo.full_name
     strategy:
       fail-fast: false
       matrix:
@@ -24,18 +25,13 @@ jobs:
         - python-version: "3.10"
           env:
             TOXENV: py
-        - python-version: "3.7"
+        - python-version: "3.10"
           env:
             TOXENV: mypy
 
     steps:
     - uses: actions/checkout@v3
 
-    - name: Install system libraries
-      if: contains(matrix.python-version, 'pypy3.9')
-      run: |
-        sudo apt-get update
-        sudo apt-get install libxml2-dev libxslt-dev
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v4
       with: