[ci] Cache pip deps

Author: nemesifier

.github/workflows/ci.yml

@@ -14,7 +14,7 @@ on:
 jobs:
   build:
     name: Python==${{ matrix.python-version }} | ${{ matrix.django-version }}
-    # Updated this only when support for Django 3.2 is removed
+    # Update this only when support for Django 3.2 is removed
     runs-on: ubuntu-20.04
 
     services:
@@ -44,6 +44,9 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: ${{ matrix.python-version }}
+          cache: 'pip'
+          cache-dependency-path: |
+            **/requirements*.txt
 
       - name: Install Dependencies & Start InfluxDB Container
         id: deps