Fix venv requirement of power graph action/power update

.forgejo/workflows/power-graph.yml

@@ -2,10 +2,8 @@ name: Generate Power Graph
 
 on:
   push:
-    branches:
-      - master
-    paths:
-      - power_log.csv
+    branches: [ master ]
+    paths: [ power_log.csv ]
 
 jobs:
   plot:
@@ -19,15 +17,19 @@ jobs:
           git clone --branch "$BRANCH" https://${{ secrets.PAT_READ_REPO }}@mentalnet.xyz/forgejo/markmental/amd-monitor.git .
           echo "✅ Checked out branch $BRANCH ($COMMIT)"
 
-      - name: Install Python dependencies
+      - name: Install Python and deps (venv)
         run: |
-          apt update
-          apt install -y python3 python3-pip
-          pip3 install matplotlib pandas
+          apt-get update
+          apt-get install -y python3-full python3-venv
+          python3 -m venv venv
+          . venv/bin/activate
+          pip install --upgrade pip
+          pip install matplotlib pandas
 
       - name: Generate power graph
         run: |
-          python3 plot_power.py
+          . venv/bin/activate
+          python plot_power.py
 
       - name: Upload graph artifact
         uses: actions/upload-artifact@v3