fix(mock-doc): add inert to HTMLAttributes (#5072)

add `inert` to the `HTMLAttributes` interface. this change only allows
the attribute to properly type check in TSX. it does not polyfill the
functionality for browsers that do not support `inert`.

STENCIL-1011 bug: Property 'inert' does not exist on type 'HTMLAttributes<HTMLXElement>'

fixes: #5071

src/declarations/stencil-public-runtime.ts

@@ -1358,6 +1358,7 @@ export namespace JSXBase {
     draggable?: boolean;
     hidden?: boolean;
     id?: string;
+    inert?: boolean;
     lang?: string;
     spellcheck?: 'true' | 'false' | any;
     style?: { [key: string]: string | undefined };