treat warnings as errors in example app

this is redundant because we already do it in the build script, but it's
nice for local development

Example/AblyChatExample.xcodeproj/project.pbxproj

@@ -206,6 +206,7 @@
 					"DEBUG=1",
 					"$(inherited)",
 				);
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
 				GCC_WARN_UNDECLARED_SELECTOR = YES;
@@ -219,6 +220,7 @@
 				SWIFT_ACTIVE_COMPILATION_CONDITIONS = "DEBUG $(inherited)";
 				SWIFT_OPTIMIZATION_LEVEL = "-Onone";
 				SWIFT_STRICT_CONCURRENCY = complete;
+				SWIFT_TREAT_WARNINGS_AS_ERRORS = YES;
 			};
 			name = Debug;
 		};
@@ -262,6 +264,7 @@
 				ENABLE_USER_SCRIPT_SANDBOXING = YES;
 				GCC_C_LANGUAGE_STANDARD = gnu17;
 				GCC_NO_COMMON_BLOCKS = YES;
+				GCC_TREAT_WARNINGS_AS_ERRORS = YES;
 				GCC_WARN_64_TO_32_BIT_CONVERSION = YES;
 				GCC_WARN_ABOUT_RETURN_TYPE = YES_ERROR;
 				GCC_WARN_UNDECLARED_SELECTOR = YES;
@@ -273,6 +276,7 @@
 				MTL_FAST_MATH = YES;
 				SWIFT_COMPILATION_MODE = wholemodule;
 				SWIFT_STRICT_CONCURRENCY = complete;
+				SWIFT_TREAT_WARNINGS_AS_ERRORS = YES;
 			};
 			name = Release;
 		};