fix(api.js): Change cb type in mockIPC to return unknown

[FabianLars]

this is a partial revert of the type changes in #8534 to fix #11720

at first i kept around the T in something like T | unknown but in my testing i didn't see any use of mockIPC that wouldn't work with the T now.

[github-actions]

Package Changes Through 9c8ecb8

There are 8 changes which include tauri-bundler with minor, tauri-cli with minor, @tauri-apps/cli with minor, tauri with minor, tauri-runtime with minor, tauri-runtime-wry with minor, @tauri-apps/api with patch, tauri-utils with patch

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
@tauri-apps/api	2.1.1	2.1.2
tauri-utils	2.1.0	2.1.1
tauri-bundler	2.1.0	2.2.0
tauri-runtime	2.2.0	2.3.0
tauri-runtime-wry	2.2.0	2.3.0
tauri-codegen	2.0.3	2.0.4
tauri-macros	2.0.3	2.0.4
tauri-plugin	2.0.3	2.0.4
tauri-build	2.0.3	2.0.4
tauri	2.1.1	2.2.0
@tauri-apps/cli	2.1.0	2.2.0
tauri-cli	2.1.0	2.2.0

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