actions/exec: add timeout option to exec function

[rhysd]

Fixes #1777

[rhysd]

The test on macOS failed but the failure seems not related to this PR's change:

Summary of all failing tests
FAIL packages/http-client/__tests__/basics.test.ts (5.499 s)
  ● basics › does basic http post request

    expect(received).toBe(expected) // Object.is equality

    Expected: 200
    Received: 502

      252 |       b
      253 |     )
    > 254 |     expect(res.message.statusCode).toBe(200)
          |                                    ^
      255 |     const body: string = await res.readBody()
      256 |     const obj = JSON.parse(body)
      257 |     expect(obj.data).toBe(b)

      at packages/http-client/__tests__/basics.test.ts:254:36
      at fulfilled (packages/http-client/__tests__/basics.test.ts:29:58)


Test Suites: 1 failed, 50 passed, 51 total
Tests:       1 failed, 572 passed, 573 total

https://github.com/actions/toolkit/actions/runs/10130893260/job/28012870699?pr=1778