Fix GCC warning about potential stringop-overflow in AudioEffectPitchShift

Fixes godotengine#101236.

Author: akien-mga

servers/audio/effects/audio_effect_pitch_shift.h

@@ -77,7 +77,7 @@ class AudioEffectPitchShift : public AudioEffect {
 public:
 	friend class AudioEffectPitchShiftInstance;
 
-	enum FFTSize {
+	enum FFTSize : unsigned int {
 		FFT_SIZE_256,
 		FFT_SIZE_512,
 		FFT_SIZE_1024,