Never pass a signed char to ctype macros like isdigit()

Bug: None
Change-Id: I451bb2c1f175a77aefbc8363009bf35a769fe941
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/264442
Reviewed-by: Tomas Gunnarsson <tommi@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37037}

modules/audio_coding/codecs/isac/main/test/ReleaseTest-API/ReleaseTest-API.cc

@@ -286,7 +286,7 @@ int main(int argc, char* argv[]) {
 
     /* Packet loss test */
     if (!strcmp("-PL", argv[i])) {
-      if (isdigit(*argv[i + 1])) {
+      if (isdigit(static_cast<unsigned char>(*argv[i + 1]))) {
         packetLossPercent = atoi(argv[i + 1]);
         if ((packetLossPercent < 0) | (packetLossPercent > 100)) {
           printf("\nInvalid packet loss perentage \n");

modules/audio_coding/codecs/isac/main/test/simpleKenny.c

@@ -22,7 +22,6 @@
 #endif
 #endif
 
-#include <ctype.h>
 #include <math.h>
 
 /* include API */