🐛(export) fix heading 4 5 6 in PDF

Heading 4 5 6 in PDF were not correctly
mapped to their corresponding styles in the
exported document.
The new export is now different than the regression
pdf, we need to update the regression PDF to match
the new correct export.

Author: AntoLC

src/frontend/apps/e2e/__tests__/app-impress/assets/doc-export-regressions.pdf

@@ -1,3 +1,7 @@
+/**
+ * Derivated from Blockquote PDF mapping
+ * @see: https://github.com/TypeCellOS/BlockNote/blob/main/packages/xl-pdf-exporter/src/pdf/defaultSchema/blocks.tsx
+ */
 import { Text } from '@react-pdf/renderer';
 
 import { DocsExporterPDF } from '../types';
@@ -30,6 +34,15 @@ export const blockMappingHeadingPDF: DocsExporterPDF['mappings']['blockMapping']
     const fontSizeEM =
       block.props.level === 1 ? 2 : block.props.level === 2 ? 1.5 : 1.17;
 
+    const levelFontSizeEM = {
+      1: 2,
+      2: 1.5,
+      3: 1.17,
+      4: 1,
+      5: 0.83,
+      6: 0.67,
+    }[block.props.level as 1 | 2 | 3 | 4 | 5 | 6];
+
     // Extract plain text for bookmark title
     const bookmarkTitle =
       extractTextFromBlockContent(block.content) || 'Untitled';
@@ -42,7 +55,7 @@ export const blockMappingHeadingPDF: DocsExporterPDF['mappings']['blockMapping']
           title: bookmarkTitle,
         }}
         style={{
-          fontSize: fontSizeEM * FONT_SIZE * PIXELS_PER_POINT,
+          fontSize: levelFontSizeEM * FONT_SIZE * PIXELS_PER_POINT,
           fontWeight: 700,
           marginTop: `${fontSizeEM * MERGE_RATIO}px`,
           marginBottom: `${fontSizeEM * MERGE_RATIO}px`,