removed piepnv env variable

While we moved from pipenv to poetry, we forgot to remove the env variable. Removing that here

Author: chinmayshah99

.github/workflows/tests.yml

@@ -29,10 +29,6 @@ jobs:
       uses: actions/setup-python@v1
       with:
         python-version: ${{ matrix.python-version }}
-    - name: Set environment variables
-      uses: allenevans/[email protected]
-      with:
-        PIPENV_DEFAULT_PYTHON_VERSION: ${{ matrix.python-version }}
     - name: Setup Bazel
       uses: abhinavsingh/setup-bazel@v3
     - name: Build PyDP with coverage