fix(a11y): do not warn if href value is dynamic (#6110)

src/compiler/compile/nodes/Attribute.ts

@@ -96,7 +96,7 @@ export default class Attribute extends Node {
 	}
 
 	get_static_value() {
-		if (this.is_spread || this.dependencies.size > 0) return null;
+		if (!this.is_static) return null;
 
 		return this.is_true
 			? true

test/validator/samples/a11y-anchor-has-content/input.svelte

@@ -1 +1,2 @@
 <a href='/foo'></a>
+<a href="#{'foo'}">bar</a>