Nesting blocks into non-comment blocks should fail.

-- Expect stderr --
Syntax error: Template blocks may not be nested
In line 2, byte 61:

 `We may not nest statement blocks into expression blocks: {{ {% print(1 + 2) %} }}.`
  Near here --------------------------------------------------^


Syntax error: Template blocks may not be nested
In line 3, byte 61:

 `We may not nest expression blocks into statement blocks: {% {{ 1 + 2 }} %}.`
  Near here --------------------------------------------------^


-- End --

-- Testcase --
We can nest other block types into comments: {# {% {{ 1 + 2 }} %} #}
We may not nest statement blocks into expression blocks: {{ {% print(1 + 2) %} }}.
We may not nest expression blocks into statement blocks: {% {{ 1 + 2 }} %}.
-- End --