Misleading info on memory usage for ZipArchiveMode.Update

### Type of issue

Missing information

### Description

I think the comment regarding ZipArchiveMode.Update is misleading. The comment gives the impression that the entire archive is loaded into memory when it is opened, but this is not true right, it just holds new and modified entries in memory until the object is disposed.

### Page URL

https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.ziparchivemode?view=net-9.0

### Content source URL

https://github.com/dotnet/dotnet-api-docs/blob/main/xml/System.IO.Compression/ZipArchiveMode.xml

### Document Version Independent Id

7c2e0ed8-6f26-aeac-8dd1-5170e67a36c9

### Article author

@dotnet-bot