Fix randomly failing test.

Fix randomly failing test.

diff --git a/lib/active_record/connection_adapters/postgresql_fallback_adapter.rb b/lib/active_record/connection_adapters/postgresql_fallback_adapter.rb
index bb2d75b..857cc28 100644
--- a/lib/active_record/connection_adapters/postgresql_fallback_adapter.rb
+++ b/lib/active_record/connection_adapters/postgresql_fallback_adapter.rb
@@ -74,6 +74,7 @@ class PostgreSQLFallbackHandler
       @master[db] = true
       @running[db] = false
       @mutex[db] = Mutex.new
+      @last_check[db] = nil
     end
   end

GitHub sha: d783a393