docs: update instance prices (#1127)

### Motivation
I need a change in `/infra/` so the github action picked it up and run
the deployment
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### Modifications

update instance prices doc
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### Verification

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Author: paulfouquet

infra/eks/cluster.ts

@@ -66,7 +66,7 @@ export class LinzEksCluster extends Stack {
 
     const nodeGroup = this.cluster.addNodegroupCapacity('ClusterDefault', {
       /**
-       * c6i.large: ~$70/month, t3.small: ~$12/month.
+       * c6i.large: ~US$60/month, t3.small: ~US$15/month.
        * Compare instance types and costs at https://instances.vantage.sh/
        * Instances are requested in order listed.
        * https://docs.aws.amazon.com/eks/latest/userguide/managed-node-groups.html#managed-node-group-capacity-types