util/abuild: Disable shellcheck warning on interrupt()

Shellcheck warns that the interrupt() function is unreachable, but it's
set to run on CTL-C. Disable the warning.

Change-Id: I0b850573964c732b1a3875dfdc7c1f0d406bac1a
Signed-off-by: Martin Roth <gaumless@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/87371
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

util/abuild/abuild

@@ -103,6 +103,7 @@ ts_basetime_str=$(date -u --date=@${ts_exec_shell})
 
 trap interrupt INT
 
+# shellcheck disable=SC2317 # Disable unreacheable code warning. It's a trap!
 interrupt()
 {
 	printf "\n%s: execution interrupted manually.\n" "$0"