Fix 6.8 ABI break: missing symbol QPageLayout::setBottomMargin()

This was forgotten when the other set*Margin() methods were moved to
removed_api in 6c72080f26.

Fixes: QTBUG-126374
Change-Id: I4be96c23540fac812ddb456699218bc437c4a3f7
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
(cherry picked from commit ad922bbac1d65ff044c63160c73324fa27f44793)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/gui/compat/removed_api.cpp

@@ -63,6 +63,11 @@ bool QPageLayout::setTopMargin(qreal topMargin)
     return setTopMargin(topMargin, OutOfBoundsPolicy::Reject);
 }
 
+bool QPageLayout::setBottomMargin(qreal bottomMargin)
+{
+    return setBottomMargin(bottomMargin, OutOfBoundsPolicy::Reject);
+}
+
 // #include "qotherheader.h"
 // // implement removed functions from qotherheader.h
 // order sections alphabetically