versions: default ARCHIVE_DATABASE_URL to DATABASE_URL.

Make it so that when ARCHIVE_DATABASE_URL isn't set, it defaults to
DATABASE_URL. In other words, if you don't have a separate archive
database configured, then default to using the main database for
post/pool versions.

Fixes an issue where running the test suite would fail if you didn't
explicitly set ARCHIVE_DATABASE_URL because it tried to use
`archive_test` as the post/pool versions database name.

.github/workflows/test.yaml

@@ -37,7 +37,6 @@ jobs:
       CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
 
       DATABASE_URL: postgresql://danbooru:danbooru@postgres/danbooru
-      ARCHIVE_DATABASE_URL: postgresql://danbooru:danbooru@postgres/danbooru
       DANBOORU_SECRET_KEY_BASE: 1234
       DANBOORU_AWS_SQS_ENABLED: false
       DANBOORU_TWITTER_API_KEY: ${{ secrets.DANBOORU_TWITTER_API_KEY }}

app/models/pool_version.rb

@@ -7,7 +7,7 @@ class PoolVersion < ApplicationRecord
   end
 
   def self.database_url
-    ENV["ARCHIVE_DATABASE_URL"] || "archive_#{Rails.env}".to_sym
+    ENV["ARCHIVE_DATABASE_URL"] || ENV["DATABASE_URL"]
   end
 
   establish_connection database_url if enabled?

app/models/post_version.rb

@@ -10,7 +10,7 @@ class PostVersion < ApplicationRecord
   end
 
   def self.database_url
-    ENV["ARCHIVE_DATABASE_URL"] || "archive_#{Rails.env}".to_sym
+    ENV["ARCHIVE_DATABASE_URL"] || ENV["DATABASE_URL"]
   end
 
   establish_connection database_url if enabled?