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[bot]]

Package Changes Through 9c8ecb85539c84df2cf8f5c6ba0a507925854db8

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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