fix venv path

Author: FoamyGuy

Diff for: .github/workflows/build-images.yml

@@ -16,7 +16,7 @@ jobs:
     - run: python3 -m venv build_images_venv
     - name: Activate virtualenv
       run: |
-        . .build_images_venv/bin/activate
+        . build_images_venv/bin/activate
         echo PATH=$PATH >> $GITHUB_ENV
     - run: python3 -mpip install -r requirements.txt
     - run: git clone --depth=1 https://github.com/adafruit/Adafruit_Learning_System_Guides learn