fix(packer): bump boot_wait default from 10s to 30s

On slower hosts (e.g. EC2-based self-hosted runners), the VM does not
reach the GRUB menu within 10 seconds, so the boot_command keystrokes
are partially lost: the initial `e` (edit entry) is eaten, the
subsequent `<down><down>` moves the *menu* selection to "Rescue an
AlmaLinux system" instead of navigating the entry editor, and the build
hangs at the GRUB menu until ssh_timeout.

30s still fits comfortably within the ISO's GRUB menu auto-boot timeout
(60s), so the keystrokes land while the menu is up on both fast and
slow hosts. The only cost is +20s per ISO build on fast runners.

Author: yuravk

variables.pkr.hcl

@@ -137,7 +137,7 @@ variable "boot_wait" {
   description = "Time to wait before typing boot command"
 
   type    = string
-  default = "10s"
+  default = "30s"
 }
 
 variable "cpus" {