[gh actions] Reduce windows build matrix

The current rdflib dependency causes random issues on some of
the github actions windows builds; since the appveyor builds
are passing without any issue, keep most gh actions windows
builds deactivated until the rdflib dependency has been
been updated.

Author: mpsonntag

.github/workflows/run-tests.yml

@@ -48,13 +48,18 @@ jobs:
           pip install -r requirements-test.txt
       - name: Run tests
         run: pytest
+# The current rdflib dependency causes random issues on some of
+# the github actions windows builds; since the appveyor builds
+# are passing without any issue, keep most gh actions windows
+# builds deactivated until the rdflib dependency has been
+# been updated.
   win_tests:
     continue-on-error: true
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
         os: [windows-latest]
-        python-version: ["3.6", "3.7", "3.8", "3.9", "3.10"]
+        python-version: ["3.10"]
     steps:
       - uses: actions/checkout@v2
       - name: Setup Python ${{ matrix.python-version }}