fix(expense): add type annotation to make_expense_claim target_doc

Backport of !2404 (merged) onto v5-fix.

Problem

Bulk submission of Expense documents fails with FrappeTypeError. Each submit triggers the Après validation des dépenses server script, which calls the whitelisted make_expense_claim.

Root cause

Frappe enforces type checking on whitelisted functions: once one argument is annotated (source_name: str), all arguments must be. target_doc had no annotation, so make_expense_claim raised before its body ran:

FrappeTypeError: Argument 'target_doc' in 'hrms.hr.doctype.expense.expense.make_expense_claim' is missing type annotation.

Fix

Annotate target_doc as str | Document | None = None and the return type as Document, matching the convention already used by the other make_* mappers in HRMS. Document was already imported.