[strict-route-types] Don't reject `number` in `config.api.bodyParser.sizeLimit` when validating route (#87633)
Not flagged behind `experimental.strictRouteTypes`. This is just a bug fix.
Got revealed once we typechecked routes in pure Pages Router apps e.g.
```
.next/types/validator.ts:76:11
Type error: Type 'typeof import("~/pages/api/hello")' does not satisfy the expected type 'ApiRouteConfig'.
The types of 'config.api.bodyParser' are incompatible between these types.
Type 'false | { sizeLimit?: SizeLimit; }' is not assignable to type 'boolean | { sizeLimit?: string; }'.
Type '{ sizeLimit?: SizeLimit; }' is not assignable to type 'boolean | { sizeLimit?: string; }'.
Type '{ sizeLimit?: SizeLimit; }' is not assignable to type '{ sizeLimit?: string; }'.
Types of property 'sizeLimit' are incompatible.
Type 'SizeLimit' is not assignable to type 'string'.
Type 'number' is not assignable to type 'string'.
```
-- https://github.com/vercel/next.js/actions/runs/20427462435/job/58690778302?pr=87628#step:32:562
Closes https://linear.app/vercel/issue/NXT-121