.git-blame-ignore-revs: sys/kern/kern_cpu.c whitespace changes

Event:          Halifax Hackathon 202606
Location:       jrm@'s kitchen
Sponsored by:   The FreeBSD Foundation

(cherry picked from commit 5f43a84d04)

.git-blame-ignore-revs

@@ -8,6 +8,8 @@
 #
 # This file is sorted in git log order (newest commits first).
 
+# sys/kern/kern_cpu.c whitespace
+XXX
 # witness white space cleanup and style(9) tweeks
 91c0ef0f5a2afa17489b603a2f82edaa28e3cce7
 # iflib style tweaks