fix(macos): accept 8-bit integer PCM microphone input

decodeInterleavedStereo's guard allowed bitsPerChannel down to 8 but
required bytesPerSample >= 2, so an 8-bit-in-1-byte microphone buffer
was rejected even though the decode loop already handles any
bytesPerSample generically. Widen the guard to 1...4 and cover it with
an 8-bit fixture.

Author: EtienneLescot

electron/native/screencapturekit/Sources/OpenScreenCaptureCore/AudioTrackMixer.swift

@@ -505,7 +505,7 @@ public final class AudioTrackMixer {
 			sourceFrames > 0,
 			isFloat
 				? bitsPerChannel == 32 && bytesPerSample == 4
-				: (8...32).contains(bitsPerChannel) && (2...4).contains(bytesPerSample)
+				: (8...32).contains(bitsPerChannel) && (1...4).contains(bytesPerSample)
 					&& bitsPerChannel <= bytesPerSample * 8
 		else {
 			return nil

electron/native/screencapturekit/Tests/OpenScreenCaptureCoreTests/AudioTrackMixerTests.swift

@@ -463,6 +463,7 @@ final class AudioTrackMixerTests: XCTestCase {
 	/// level and with the right sign.
 	func testIntegerMicrophoneFormatsAreHeardAtTheirLevel() {
 		let layouts: [(bits: Int, bytes: Int, alignedHigh: Bool, signed: Bool, label: String)] = [
+			(8, 1, false, true, "8-bit"),
 			(24, 3, false, true, "24-bit packed (the reported format)"),
 			(24, 4, false, true, "24-bit in 4 bytes, low-aligned"),
 			(24, 4, true, true, "24-bit in 4 bytes, high-aligned"),