tests: avoid docker hub busybox pulls in readonly tmt cases

Agent-Logs-Url: https://github.com/bootc-dev/bootc/sessions/922a86aa-023b-4d6a-9af6-766b564e1179

Co-authored-by: cgwalters <244096+cgwalters@users.noreply.github.com>

Author: Copilot

tmt/tests/booted/readonly/010-test-bootc-container-store.nu

@@ -33,8 +33,9 @@ if not $has_storage {
     # And verify this works
     bootc image cmd list -q o>/dev/null
 
-    bootc image cmd pull busybox
-    podman --storage-opt=additionalimagestore=/usr/lib/bootc/storage image exists busybox
+    let public_test_image = "quay.io/libpod/busybox:latest"
+    bootc image cmd pull $public_test_image
+    podman --storage-opt=additionalimagestore=/usr/lib/bootc/storage image exists $public_test_image
 
     # Images in bootc storage should be listed with type "unified"
     let images = bootc image list --format json | from json

tmt/tests/booted/readonly/030-test-composefs.nu

@@ -56,7 +56,7 @@ if $is_composefs {
     # we can't get from `bootc internals cfs ...`
     mkdir /var/tmp/sysroot/composefs
     bootc internals cfs --insecure --repo /var/tmp/sysroot/composefs init
-    bootc internals cfs --insecure --repo /var/tmp/sysroot/composefs oci pull docker://busybox busybox
+    bootc internals cfs --insecure --repo /var/tmp/sysroot/composefs oci pull docker://quay.io/libpod/busybox:latest busybox
     test -L /var/tmp/sysroot/composefs/streams/refs/oci/busybox
 }