fix: add ecr auth to GitHub Actions role (#361)

Need to give permissions for the GitHub Actions role to read the ECR
authorization token such that it can auth to push and pull from the
repo.

Signed-off-by: Gavin Inglis <giinglis@amazon.com>

lib/continuous-integration-stack.ts

@@ -50,6 +50,7 @@ export class ContinuousIntegrationStack extends cdk.Stack {
 
     const repo = props.rootfsEcrRepository;
     repo.grantPullPush(githubActionsRole);
+    ecr.AuthorizationToken.grantRead(githubActionsRole)
 
     new CloudfrontCdn(this, 'DependenciesCloudfrontCdn', {
       bucket