can't watch added files when entry is  `entry: "src/**/*.ts"`

### Reproduction link or steps

1. set `entry: "src/**/*.ts"` in `tsdown.config.ts`
2. set `"dev": "tsdown --watch ./src",`
3. `npm run dev`  
4. add file `src/a.ts`

expected to re-build and generate `dist/a.ts`, but not




### What is expected?

expected to re-build and generate `dist/a.ts`

### What is actually happening?

no rebuild

### Any additional comments?

_No response_