Don't use container-env file; run builds every night if changes

.github/workflows/build-deploy-pudl.yml

@@ -5,7 +5,9 @@ on:
     tags:
       - "v20*"
   schedule:
-    - cron: "0 6 * * 1-5" # Weekdays at midnight on MST
+    # 6am UTC daily (11pm PDT, 2am EDT)
+    # But only if there are changes since the last nightly build.
+    - cron: "0 6 * * *"
 
 env:
   GCP_BILLING_PROJECT: ${{ secrets.GCP_BILLING_PROJECT }}
@@ -133,7 +135,6 @@ jobs:
             --container-arg='' \
             --container-arg="bash" \
             --container-arg="./docker/gcp_pudl_etl.sh" \
-            --container-env-file="./docker/.env" \
             --container-env BUILD_REF=${{ github.ref_name }} \
             --container-env BUILD_ID=${{ env.BUILD_ID }} \
             --container-env NIGHTLY_TAG=${{ env.NIGHTLY_TAG }} \