fix(trends): Chart title background overlapping panel border (#26145)

This fixes a few pixels missing from the trends panel because of the title header overlapping it.

static/app/views/performance/trends/changedTransactions.tsx

@@ -545,6 +545,7 @@ const ChartContainer = styled('div')`
 `;
 
 const StyledHeaderTitleLegend = styled(HeaderTitleLegend)`
+  border-radius: ${p => p.theme.borderRadius};
   padding: ${space(2)} ${space(3)};
 `;