Fix build test

TinyGsmClientA6.h

@@ -406,7 +406,7 @@ public:
     return waitResponse() == 1;
   }
 
-  void callRedial() {
+  bool callRedial() {
     sendAT(GF("DLST"));
     return waitResponse() == 1;
   }

TinyGsmClientM590.h

@@ -405,7 +405,7 @@ public:
     return waitResponse() == 1;
   }
 
-  void callRedial() TINY_GSM_ATTR_NOT_AVAILABLE;
+  bool callRedial() TINY_GSM_ATTR_NOT_AVAILABLE;
 
   bool callHangup(const String& number) {
     sendAT(GF("H"), number);

TinyGsmClientSIM800.h

@@ -498,7 +498,7 @@ public:
     return waitResponse() == 1;
   }
 
-  void callRedial() {
+  bool callRedial() {
     sendAT(GF("DL"));
     return waitResponse() == 1;
   }