patches: fix invalid placeholder SHA in danctnix cover letter

The danctnix-series cover letter had an invalid 41-hex-char
placeholder SHA on its 'From' header line (40 zeros with an
f1d22ab0 prefix) -- a relic of manual generation. Replaced with
the valid 40-char SHA already used by the Mobian-series cover
letter. The value is cosmetic (cover letters aren't real commits)
but an invalid SHA will confuse 'git am'.

patches/staging-prep-series-danctnix/0000-cover-letter.patch

@@ -1,4 +1,4 @@
-From f1d22ab0000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From 6f13e008d21d453db486f707f47340a0a17e650b Mon Sep 17 00:00:00 2001
 From: Markus Fritsche <fritsche.markus@gmail.com>
 Date: Wed, 22 Apr 2026 14:27:00 +0200
 Subject: [PATCH 0/6] bes2600: staging-prep cleanup for PineTab2 (BES2600WM)