Add test for kill 0

Author: psznm

lib/std/posix/test.zig

@@ -980,3 +980,12 @@ const CommonOpenFlags = packed struct {
         return result;
     }
 };
+
+test "kill 0 can be used to perform checks of sending signal" {
+    if (native_os == .wasi) return error.SkipZigTest;
+    if (native_os == .windows) return error.SkipZigTest;
+    posix.kill(posix.getpid(), .INVAL) catch |err| switch (err) {
+        posix.KillError.PermissionDenied => return,
+        else => return err,
+    };
+}