Update the CHANGELOG for 6.6.3

CHANGELOG.TXT

@@ -1,5 +1,16 @@
 6.6.3 (2023-09-06)
-	- See https://github.com/tecnickcom/TCPDF/commits/main
+	- Fix SPDX license ID (#591)
+	- Fix warning "array offset on value of type null" (#620)
+	- Improve the README about the status of this library (#589)
+	- Fix deprecation warning with PHP 8.1 (#614)
+	- Fixes for PHP 8.2 in tcpdf_fonts.php (#632)
+	- Fix some php 8+ edge cases (#630)
+	- Fix composite glyph output (#581)
+	- Fix "access array offset on value of type bool" with PDF/A (#583)
+	- Fix non-numeric value warning (#627)
+	- Fix issues with S25 barcode (#611)
+	- Fix return type annotations (#613)
+	- Fix some inconsistencies in type hints (#598)
 
 6.6.2 (2022-12-17)
 	- Ensure pregSplit return type is always array.