fix(api.js): Change cb type in mockIPC to return unknown (#11724) #11940

Job	Run time
test (x86_64-pc-windows-msvc, windows-latest, 1.77.2, false, test, --no-default-features, no-defa...	6m 18s
test (x86_64-pc-windows-msvc, windows-latest, 1.77.2, false, test, --all-features, all)	8m 45s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.77.2, false, test, --no-default-features, no-def...	4m 56s
test (x86_64-unknown-linux-gnu, ubuntu-latest, 1.77.2, false, test, --all-features, all)	7m 37s
test (aarch64-apple-darwin, macos-14, 1.77.2, false, test, --no-default-features, no-default)	2m 31s
test (aarch64-apple-darwin, macos-14, 1.77.2, false, test, --all-features, all)	2m 42s
test (aarch64-apple-ios, macos-latest, 1.77.2, false, build, --no-default-features, no-default)	1m 56s
test (aarch64-apple-ios, macos-latest, 1.77.2, false, build, --all-features, all)	1m 31s
test (aarch64-linux-android, ubuntu-latest, 1.77.2, true, build, --no-default-features, no-default)	2m 57s
test (aarch64-linux-android, ubuntu-latest, 1.77.2, true, build, --all-features, all)	4m 26s
	43m 39s

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