[compilation] PS-9380: Fix clang-12+ compilation issues

```
../../../storage/innobase/btr/btr0mtib.cc:962:36: error: lambda capture 'this' is not used [-Werror,-Wunused-lambda-capture]
  auto guard = create_scope_guard([this, page_no]() {
                                   ^~~~~
../../../storage/innobase/btr/btr0mtib.cc:962:42: error: lambda capture 'page_no' is not used [-Werror,-Wunused-lambda-capture]
  auto guard = create_scope_guard([this, page_no]() {
                                       ~~^~~~~~~
```

storage/innobase/btr/btr0mtib.cc

@@ -959,6 +959,7 @@ dberr_t Page_load::init_mem_blob(const page_no_t page_no,
   ut_ad(page_no < page_extent->m_range.second);
   ut_ad(m_heap == nullptr);
 
+#ifndef NDEBUG
   auto guard = create_scope_guard([this, page_no]() {
     ut_ad(m_block != nullptr);
     ut_ad(m_mtr == nullptr);
@@ -967,6 +968,7 @@ dberr_t Page_load::init_mem_blob(const page_no_t page_no,
     ut_ad(m_page_no != FIL_NULL);
     ut_ad(m_page_no == page_no);
   });
+#endif
 
   m_page_extent = page_extent;
   m_page_no = page_no;