chore: migrate to ESLint 9 and update configurations

src/issue.ts

@@ -2,8 +2,8 @@ import * as core from '@actions/core'
 import {IssueOption} from './interface.js'
 
 export function getIssueOption(body: string): IssueOption {
-  let assignees
-  let labels
+  let assignees: string[] | undefined
+  let labels: string[] | undefined
 
   if (core.getInput('issue_assignees')) {
     assignees = core.getInput('issue_assignees').replace(/\s+/g, '').split(',')
@@ -29,7 +29,7 @@ export type GetIssuesFunc = (options: {
   state: 'open' | 'closed' | 'all' | undefined
   // eslint-disable-next-line @typescript-eslint/no-explicit-any
   [key: string]: any // Allow additional properties
-}) => Promise<{data: {title: string; number: number}[]}>
+}) => Promise<{data: Array<{title: string; number: number}>}>
 
 export async function getExistingIssueNumber(
   getIssues: GetIssuesFunc,