Simplify CI test installation

Author: xmatthias

.github/workflows/tests.yml

@@ -20,10 +20,9 @@ jobs:
         python-version: ${{ matrix.python-version }}
     - name: Install dependencies
       run: |
-        python -m pip install --upgrade pip wheel
-        python -m pip install -r requirements.txt
-        python -m pip install -r requirements_test.txt
-        pip install flake8 pytest
+        pip install --upgrade pip wheel
+        pip install -r requirements_test.txt
+        pip install flake8
         ./tools/build_talib_from_source.bash $DEPS_PATH
       env:
         DEPS_PATH: ${{ github.workspace }}/dependencies