ci: pin harness test dependency

Author: KooshaPari

.github/workflows/ci.yml

@@ -113,7 +113,7 @@ jobs:
         with:
           python-version: "3.12"
       - name: Install harness test dependencies
-        run: python -m pip install --disable-pip-version-check --quiet -e harness pytest
+        run: python -m pip install --disable-pip-version-check --quiet -e harness 'pytest==8.4.1'
       - name: Harness envelope and replay contracts
         env:
           PYTEST_DISABLE_PLUGIN_AUTOLOAD: "1"