Failed to resolve the module node:* when target ≠ "node"

Similar to https://github.com/developit/microbundle/issues/989, but now occurring only when Microbundle's target is not Node.js. I'm compiling a library that runs in both Node.js and a browser, and the library contains dynamic imports for node built-ins like 'fs', executed only in Node.js.

When importing `fs` I can add the following to my `package.json` and everything works fine:

```
"browser": {
"fs": false,
"path": false
},
```

However, using `node:fs`, the same thing does not work, and warnings appear with:

```
"browser": {
"node:fs": false,
"node:path": false
},
```

```
Failed to resolve the module node:fs
```

Microbundle v0.15.1, Node.js v18.12.1.

首先使用 Microbundle v0.15.1、非 Node 目標，以及 package.json 中針對 node:fs 和 node:path 的瀏覽器對應來重現問題。將其行為與針對 fs 和 path 的對應進行比較；當帶有 node 前綴的內建模組在瀏覽器相容的建置中無需警告即可解析時，即表示完成。

由索引模型根據 Issue 內容生成。