chore: update version to 3.8.9

Relates to #726

Author: YDX-2147483647

src/bithesis.dtx

@@ -21,10 +21,10 @@
 %<thesis>\ProvidesExplClass{bithesis}
 %<report>\ProvidesExplClass{bitreport}
 %<beamer>\ProvidesExplClass{bitbeamer}
-%<cls>  {2026-03-11} {3.8.8} {BIT Thesis Templates}
+%<cls>  {2026-03-31} {3.8.9} {BIT Thesis Templates}
 %
 %<*driver>
-\ProvidesFile{bithesis.dtx}[2026/03/11 v3.8.8 BIT Thesis Templates]
+\ProvidesFile{bithesis.dtx}[2026/03/31 v3.8.9 BIT Thesis Templates]
 \documentclass[letterpaper]{l3doc}
 \usepackage{dtx-style}