Bump webhook timeout. (sigstore#1465)

This is taking longer than 10s sometimes now, breaking CI.

Matt did some debugging and found it's because the distroless image we use here
has accumulated so many signatures that it takes a long time to fetch them all.

Signed-off-by: Dan Lorenc <lorenc.d@gmail.com>

config/500-webhook-configuration.yaml

@@ -31,6 +31,7 @@ webhooks:
       namespace: cosign-system
   failurePolicy: Fail
   sideEffects: None
+  timeoutSeconds: 25
 
 ---
 apiVersion: admissionregistration.k8s.io/v1
@@ -52,6 +53,7 @@ webhooks:
       namespace: cosign-system
   failurePolicy: Fail
   sideEffects: None
+  timeoutSeconds: 25
 
 ---
 apiVersion: v1