build: Update github workflows that relied on pip.txt

Use the `pre-requirements` target to ensure that pip is installed at a
version that's valid for the rest of the workflow.

.github/workflows/ci-static-analysis.yml

@@ -25,7 +25,7 @@ jobs:
         run: sudo apt update && sudo apt install -y libxmlsec1-dev
 
       - name: Install pip
-        run: python -m pip install -r requirements/pip.txt
+        run: make pre-requirements
 
       - name: Get pip cache dir
         id: pip-cache-dir

.github/workflows/lint-imports.yml

@@ -25,7 +25,7 @@ jobs:
         run: sudo apt update && sudo apt install -y libxmlsec1-dev
 
       - name: Install pip
-        run: python -m pip install -r requirements/pip.txt
+        run: make pre-requirements
 
       - name: Get pip cache dir
         id: pip-cache-dir
@@ -40,7 +40,7 @@ jobs:
           restore-keys: ${{ runner.os }}-pip-
 
       - name: Install python dependencies
-        run: pip install -r requirements/edx/development.txt
+        run: make dev-requirements
 
       # As long there are sub-projects[1] in edx-platform, we analyze each
       # project separately here, in order to make import-linting errors easier