Cache virtualenv between jobs

Installation of the python dependencies and scripts is done at the start
of each job within the build.yaml workflow.

By caching the venv we can save up to 10 seconds on each job after the
first. With the planned re-introduction of #392 that splits the
chart-verifier job into 3, this can scale to up to a total of 40s per
run.

Signed-off-by: Matthias Goerens <[email protected]>

.github/workflows/build.yml

@@ -22,6 +22,7 @@ jobs:
         uses: actions/checkout@v4
 
       - name: Set up Python 3.x Part 1
+        id: setup_python
         uses: actions/setup-python@v5
         with:
           python-version: "3.10"
@@ -35,6 +36,12 @@ jobs:
           ../ve1/bin/pip3 install .
           cd ..
 
+      - name: Saved cached virtualenv
+        uses: actions/cache/save@v4
+        with:
+          key: venv-${{ runner.os }}-${{ steps.setup_python.outputs.python-version }}-${{ hashFiles('scripts/requirements.txt') }}
+          path: ve1
+
       - name: Check for CI changes
         id: check_ci_changes
         env:
@@ -124,10 +131,17 @@ jobs:
           path: "pr-branch"
 
       - name: Set up Python 3.x Part 1
+        id: setup_python
         uses: actions/setup-python@v5
         with:
           python-version: "3.10"
 
+      - name: Restore cached virtualenv
+        uses: actions/cache/restore@v4
+        with:
+          key: venv-${{ runner.os }}-${{ steps.setup_python.outputs.python-version }}-${{ hashFiles('scripts/requirements.txt') }}
+          path: ve1
+
       - name: Set up Python 3.x Part 2
         run: |
           # set up python
@@ -429,10 +443,17 @@ jobs:
           path: "pr-branch"
 
       - name: Set up Python 3.x Part 1
+        id: setup_python
         uses: actions/setup-python@v5
         with:
           python-version: "3.10"
 
+      - name: Restore cached virtualenv
+        uses: actions/cache/restore@v4
+        with:
+          key: venv-${{ runner.os }}-${{ steps.setup_python.outputs.python-version }}-${{ hashFiles('scripts/requirements.txt') }}
+          path: ve1
+
       - name: Set up Python 3.x Part 2
         run: |
           # set up python