Bump buildah image

Buildah image in few tasks was not pointing to latest
image release tag, so updated the image to point to
latest release.

Signed-off-by: Divyansh42 <diagrawa@redhat.com>

task/aws-ecr-login/0.1/samples/test-task.yaml

@@ -16,7 +16,7 @@ spec:
       type: string
   steps:
     - name: pull-and-push
-      image: quay.io/buildah/stable:v1.14.8
+      image: quay.io/buildah/stable:v1.15.1
       script: |
         # Login to ecr
         buildah login \

task/buildah/0.1/README.md

@@ -17,7 +17,7 @@ kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/master/task/
 
 * **IMAGE**: The name (reference) of the image to build.
 * **BUILDER_IMAGE:**: The name of the image containing the Buildah tool. See
-  note below.  (_default:_ quay.io/buildah/stable:v1.11.0)
+  note below.  (_default:_ quay.io/buildah/stable:v1.15.1)
 * **DOCKERFILE**: The path to the `Dockerfile` to execute (_default:_
   `./Dockerfile`)
 * **CONTEXT**: Path to the directory to use as context (_default:_

task/buildah/0.1/buildah.yaml

@@ -24,7 +24,7 @@ spec:
     description: Reference of the image buildah will produce.
   - name: BUILDER_IMAGE
     description: The location of the buildah builder image.
-    default: quay.io/buildah/stable:v1.14.8
+    default: quay.io/buildah/stable:v1.15.1
   - name: STORAGE_DRIVER
     description: Set buildah storage driver
     default: overlay

task/s2i/0.1/s2i.yaml

@@ -61,7 +61,7 @@ spec:
     - -t
     - $(resources.outputs.image.url)
     - .
-    image: quay.io/buildah/stable
+    image: quay.io/buildah/stable:v1.15.1
     securityContext:
       privileged: true
     volumeMounts:
@@ -77,7 +77,7 @@ spec:
     - --tls-verify=$(params.TLSVERIFY)
     - $(resources.outputs.image.url)
     - docker://$(resources.outputs.image.url)
-    image: quay.io/buildah/stable
+    image: quay.io/buildah/stable:v1.15.1
     securityContext:
       privileged: true
     volumeMounts: