ci: use installed pip, upgrade to pinned if necessary

Ref: pytest-dev#6522

.github/workflows/main.yml

@@ -120,7 +120,9 @@ jobs:
         key: pre-commit|${{ env.PY_CACHE_KEY }}|${{ hashFiles('.pre-commit-config.yaml') }}
 
     - name: Install tox
-      run: python -m pip install git+https://github.com/blueyed/tox@master
+      run: |
+        python -m pip --version
+        python -m pip install git+https://github.com/blueyed/tox@master
 
     - name: Setup tox environment
       run: python -m tox --notest -v --durations -e ${{ matrix.tox_env }}
@@ -157,6 +159,7 @@ jobs:
         python-version: "3.7"
     - name: Install dependencies
       run: |
+        python -m pip --version
         python -m pip install wheel setuptools git+https://github.com/blueyed/tox@master
     - name: Build package
       run: |

.travis.yml

@@ -23,7 +23,7 @@ jobs:
       python: '3.5.1'
       dist: trusty
       before_install:
-        - python -m pip install -U pip
+        - python -m pip install -U pip==19.3.1
 
 before_script:
   - |