error: `extends` block must come first in a template
 --> <source attribute>:2:2
       " extends \"base.html\" %}\n"
 --> tests/ui/extend.rs:5:14
  |
5 |       source = r##"bla
  |  ______________^
6 | | {% extends "base.html" %}
7 | | "##,
  | |___^