Suppress unused-result warnings

* Hide read function warning in string_spec_RSTRING_PTR_read function

* The type of `read` may be `ssize_t`

Co-authored-by: Nobuyoshi Nakada <nobu@ruby-lang.org>

spec/ruby/optional/capi/ext/string_spec.c

@@ -397,12 +397,16 @@ VALUE string_spec_RSTRING_PTR_read(VALUE self, VALUE str, VALUE path) {
   rb_str_modify_expand(str, 30);
   rb_ary_push(capacities, SIZET2NUM(rb_str_capacity(str)));
   char *buffer = RSTRING_PTR(str);
-  read(fd, buffer, 30);
+  if (read(fd, buffer, 30) < 0) {
+    rb_syserr_fail(errno, "read");
+  }
 
   rb_str_modify_expand(str, 53);
   rb_ary_push(capacities, SIZET2NUM(rb_str_capacity(str)));
   char *buffer2 = RSTRING_PTR(str);
-  read(fd, buffer2 + 30, 53 - 30);
+  if (read(fd, buffer2 + 30, 53 - 30) < 0) {
+    rb_syserr_fail(errno, "read");
+  }
 
   rb_str_set_len(str, 53);
   close(fd);