Fix header color of stat item

The header color of a stat item was using the badge foreground color,
but badges can have a different background color than the editor. For
some themes, this would result in unreadable text. By using the editor
foreground color, the header should be readable in many more themes.

extensions/ql-vscode/src/view/variant-analysis/StatItem.tsx

@@ -12,7 +12,7 @@ const Container = styled.div`
 `;
 
 const Header = styled.div`
-  color: var(--vscode-badge-foreground);
+  color: var(--vscode-editor-foreground);
   font-size: 0.85em;
   font-weight: 800;
   text-transform: uppercase;