Fix and rename build date

- rename from BASE_BUILD_DATE to BASE_CREATED to match label name
- noticed it wasn't a valid utc iso timestamp, so fixed that
- noticed we are using a weird hybrid of make and just, so fixed that

.github/workflows/tests.yaml

@@ -9,9 +9,9 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@master
+    - uses: extractions/setup-just@69d82fb0233557aec017ef13706851d0694e0f1d
     - name: Build image
       run: just build
-    - uses: extractions/setup-just@69d82fb0233557aec017ef13706851d0694e0f1d
     - name: Run tests
       run: just test
     - name: Run lint