ci: bump image-builder to include MachinePool cloud-init fix

The v1.33/v1.34 CAPA AMIs were built with image-builder v0.1.48, which
includes a custom cloud-init datasource (DataSourceEc2Kubernetes) that
unconditionally reads from /etc/secret-userdata.txt. This file is only
created by the SecretsManager boothook for individual Machine nodes
(control plane, MachineDeployment), but not for MachinePool/ASG nodes
where bootstrap data is passed directly as EC2 user-data. The missing
file causes a FileNotFoundError, crashing cloud-init and preventing
MachinePool worker nodes from joining the cluster.

Pin the image-builder version to commit 990737c (post-v0.1.48) which
adds a graceful fallback: when /etc/secret-userdata.txt is absent, the
datasource uses the original EC2 metadata user-data instead.

The affected AMIs (ubuntu v1.33.4 and v1.34.3) need to be rebuilt
with this version for the fix to take effect.

Ref: kubernetes-sigs/image-builder@990737c

Author: damdo

.github/workflows/build-ami-varsfile.yml

@@ -6,7 +6,7 @@ on:
       image_builder_version:
         description: "Image builder version"
         required: true
-        default: 'v0.1.48'
+        default: '990737c79abb37fd56faca64f46e5a385dd1a982' # post-v0.1.48, includes fix https://github.com/kubernetes-sigs/image-builder/pull/1919
       target:
         description: "target os"
         required: true

.github/workflows/build-ami.yml

@@ -6,7 +6,7 @@ on:
       image_builder_version:
         description: "Image builder version"
         required: true
-        default: 'v0.1.48'
+        default: '990737c79abb37fd56faca64f46e5a385dd1a982' # post-v0.1.48, includes fix https://github.com/kubernetes-sigs/image-builder/pull/1919
       regions:
         description: 'Publication regions'
         required: true