Add missing parameter in pip install command

.github/workflows/tests.yml

@@ -57,7 +57,7 @@ jobs:
         run: python -u -m pip install --upgrade pip setuptools ;
       - name: Install requirements from requirements.txt
         if: steps.pip-cache.outputs.cache-hit != 'true'
-        run: pip install -r requirements.txt ;
+        run: pip install --upgrade -r requirements.txt ;
       - name: Run cargo tarpaulin (code coverage for Rust code), note that macOS runs bash on CI, not zsh
         run: cargo tarpaulin --all-targets --count --exclude-files=target/* --engine=llvm --fail-under=80 --ignored --no-dead-code --out=stdout --skip-clean --target-dir=target/tarpaulin-target/ ;
       - name: Install using maturin, optimized Rust code