fix: config: vocabularies: Add fdisk & umount commands to accept.txt

This adds 'fdisk' and 'umount' to accept.txt. These are commands used
across various how-to flash guides.

Signed-off-by: Judith Mendez <jm@ti.com>

Author: jmenti

.github/styles/config/vocabularies/PSDK/accept.txt

@@ -28,3 +28,5 @@ Weston
 Trixie
 mmdebstrap
 bdebstrap
+fdisk
+umount