Stray } in element is interpreted as an attribute and causes a runtime error

[dimfeld]

Describe the bug
When Svelte sees an element with an orphaned } character it interprets the bracket as an attribute. e.g.

<h1 }>text</h1>
causes this to be generated in the create function:
attr(h1, "}", "");
and causes the runtime error
Failed to execute 'setAttribute' on 'Element': '}' is not a valid attribute name.

REPL: https://svelte.dev/repl/14ee9617902447809daec74565b61a8e?version=3.20.1

Expected behavior
IMO the compiler should throw an error instead of generating code for this.

Severity
Not too important. Was pretty obvious what happened when I looked back at my source file and saw the } character I missed deleting.

[Conduitry]

This is now a compile time error rather than a runtime one - https://svelte.dev/repl/14ee9617902447809daec74565b61a8e?version=3.21.0