--doc option seems disabling type checking

[kt3k]

Save the below script as test.ts, and then deno test throws type error at const a, but deno test --doc doesn't throw type error.

/**
 * ```ts
 * ```
 */
function foo() {}

const a: string = 1;

If I remove the code block part in the jsdoc, then this issue doesn't happen.

Version: Deno 1.42.4

[crowlKats]

After some searching, we found out that the issue is a regression from #22854. This is because of

deno/cli/module_loader.rs

Line 116 in b3d7df5

let has_type_checked = !graph.roots.is_empty();

, and because the prepare_module_load function is called twice, once for doc files and once for actual files, it does not type check because on second call has_type_checked is true.