REGRESSION(304354@main) GLIB build failure without assertions due to wrong WARN_UNUSED_RETURN

https://bugs.webkit.org/show_bug.cgi?id=304063

Reviewed by Xabier Rodriguez-Calvar.

Update the macro position, like 304354@main did.

* Source/WTF/wtf/glib/GMallocString.h:

Canonical link: https://commits.webkit.org/304358@main

Author: lauromoura

Source/WTF/wtf/glib/GMallocString.h

@@ -95,7 +95,7 @@ class GMallocString final {
 
     bool isNull() const { return m_spanWithNullTerminator.span().empty(); }
     const char* utf8() const LIFETIME_BOUND { return byteCast<char>(m_spanWithNullTerminator.span().data()); }
-    char* leakUTF8() WARN_UNUSED_RETURN { return byteCast<char>(m_spanWithNullTerminator.leakSpan().data()); }
+    WARN_UNUSED_RETURN char* leakUTF8() { return byteCast<char>(m_spanWithNullTerminator.leakSpan().data()); }
     size_t lengthInBytes() const { return !m_spanWithNullTerminator.span().empty() ? m_spanWithNullTerminator.span().size() - 1 : 0; }
     std::span<const char8_t> span() const LIFETIME_BOUND { return m_spanWithNullTerminator.span().first(lengthInBytes()); }
     std::span<const char8_t> spanIncludingNullTerminator() const LIFETIME_BOUND { return m_spanWithNullTerminator.span(); }