serverTimestamp fails when uploading to firestore.

Version info
Angular: ^17.3.0",
Firebase: 9.23.0
AngularFire: ^17.0.1",
Node v20.11.

How to reproduce these conditions
Failing test unit, Stackblitz demonstrating the problem:

Currently, I do not have a failing test unit or a Stackblitz example, but I can describe the issue and the steps to reproduce it below.

Steps to set up and reproduce:

Set up AngularFirestore and AngularFireStorage in your Angular component.
Create a form with a field set to serverTimestamp().
Attempt to update a Firestore document using WriteBatch.update() with the form values.
Here is a snippet of the code causing the issue:

```
import { serverTimestamp } from 'firebase/firestore';
import { AngularFirestore } from '@angular/fire/compat/firestore';

constructor(private afs: AngularFirestore, ...) {
this.form = this.builder.group({
dateReported: [serverTimestamp(), Validators.required],
...
});

const batch = this.afs.firestore.batch();
const orderRef = this.afs.firestore.collection(...).doc(....);
batch.update(orderRef, this.form.value);
batch.commit()
}
```
Sample data and security rules:

Please provide the necessary data structure and Firestore security rules if they are relevant to the issue.

Debug output
Errors in the JavaScript console:
```
{
"items": [
{
"sku": "2756",
"qty": 1,
"name": "\tImpresora Artillery X3 Plus"
}
],
"dateReported": {
"_methodName": "serverTimestamp"
},
"dateModified": {
"_methodName": "serverTimestamp"
},
"trialsAndResults": "cable suelto",
"inspectedItems": [
{
"sku": "2756",
"qty": 1,
"name": "\tImpresora Artillery X3 Plus",
"dictum": "repair"
}
],
"status": "examined",
"technician": "Cristobal",
"charge": 0,
"report": null
}
FirebaseError: Function WriteBatch.update() called with invalid data. Unsupported field value: a custom sl object (found in field dateReported in document [...])
```

Output from firebase.database().enableLogging(true);:

Please attach output if available.

Screenshots:

Please attach screenshots if they help illustrate the problem.

Expected behavior
The expected behavior is that the Firestore document should be updated with the current server timestamp in the dateReported field without any errors.

Actual behavior
The actual behavior is that an error is thrown when trying to update the Firestore document, indicating that an unsupported field value (a custom sl object) was found in the dateReported field.

Also there is no documentation how to use serverTimestamp, increment, etc, for current version using compat.

首先，使用列出的 Angular、Firebase、AngularFire 和 Node 版本复现提供的 AngularFirestore batch.update() 示例。将 serverTimestamp 和相关字段值的 compat 用法与当前文档进行比较；当复现过程得到解释，并且受支持的用法或所需文档明确时，即视为完成。

由索引模型根据 Issue 内容生成。