fix: do not use undefined yet, as it will not be set correctly yet

With this the test will run successful again, but show every block as
a `.tldr` one, and not based on what is actually found, as that part of
the parser has not been implemented yet.

src/parser.zig

@@ -35,7 +35,7 @@ fn parse(allocator: Allocator, content: [:0]const u8) !Ast {
             .block => break :tag .{
                 .tag = .{
                     .block = .{
-                        .kind = undefined,
+                        .kind = .tldr, // TODO parse correctly from the contents
                     },
                 },
                 .loc = token.loc,