Prevent wrong integer expansion

`(attr_index + 1)` leads to wrong integer expansion on 32-bit machines
(including Solaris 10 CI) because `attr_index_t` is uint16_t.

http://rubyci.s3.amazonaws.com/solaris10-gcc/ruby-master/log/20221013T080004Z.fail.html.gz
```
  1) Failure:
TestRDocClassModule#test_marshal_load_version_2 [/export/home/users/chkbuild/cb-gcc/tmp/build/20221013T080004Z/ruby/test/rdoc/test_rdoc_class_module.rb:493]:
<[doc: [doc (file.rb): [para: "this is a comment"]]]> expected but was
<[doc: [doc (file.rb): [para: "this is a comment"]]]>.

  2) Failure:
TestRDocStats#test_report_method_line [/export/home/users/chkbuild/cb-gcc/tmp/build/20221013T080004Z/ruby/test/rdoc/test_rdoc_stats.rb:460]:
Expected /\#\ in\ file\ file\.rb:4/ to match "The following items are not documented:\n" +
"\n" +
"  class C # is documented\n" +
"\n" +
"    # in file file.rb\n" +
"    def m1; end\n" +
"\n" +
"  end\n" +
"\n" +
"\n".

  3) Failure:
TestRDocStats#test_report_attr_line [/export/home/users/chkbuild/cb-gcc/tmp/build/20221013T080004Z/ruby/test/rdoc/test_rdoc_stats.rb:91]:
Expected /\#\ in\ file\ file\.rb:3/ to match "The following items are not documented:\n" +
"\n" +
"  class C # is documented\n" +
"\n" +
"    attr_accessor :a # in file file.rb\n" +
"\n" +
"  end\n" +
"\n" +
"\n".
```

vm_callinfo.h

@@ -457,13 +457,13 @@ vm_cc_attr_index_set(const struct rb_callcache *cc, attr_index_t index, shape_id
     }
     VM_ASSERT(IMEMO_TYPE_P(cc, imemo_callcache));
     VM_ASSERT(cc != vm_cc_empty());
-    *attr_value = (index + 1) | ((uintptr_t)(dest_shape_id) << SHAPE_FLAG_SHIFT);
+    *attr_value = (attr_index_t)(index + 1) | ((uintptr_t)(dest_shape_id) << SHAPE_FLAG_SHIFT);
 }
 
 static inline void
 vm_ic_attr_index_set(const rb_iseq_t *iseq, const struct iseq_inline_iv_cache_entry *ic, attr_index_t index, shape_id_t dest_shape_id)
 {
-    *(uintptr_t *)&ic->value = ((uintptr_t)dest_shape_id << SHAPE_FLAG_SHIFT) | (index + 1);
+    *(uintptr_t *)&ic->value = ((uintptr_t)dest_shape_id << SHAPE_FLAG_SHIFT) | (attr_index_t)(index + 1);
 }
 
 static inline void