Fix indentation bug for snips out in testing framework

[SRodi]

Description

It appears the "expected" output indentation is updated during tests execution. See https://github.com/istio/istio.io/pull/14577#discussion_r1481629850

VERIFY FAILED snip_egress_gateway_for_http_traffic_10 (timeout after 120s):
received:
"            X509v3 Subject Alternative Name: critical
                URI:spiffe://cluster.local/ns/istio-system/sa/istio-egressgateway-service-account"
expected:
"X509v3 Subject Alternative Name: critical
                URI:spiffe://cluster.local/ns/istio-system/sa/istio-egressgateway-service-account"

This is the failed output log in istio-prow https://storage.googleapis.com/istio-prow/pr-logs/pull/istio_istio.io/14577/doc.test.profile-demo_istio.io/1755243935380279296/artifacts/tests-setup-profile-demo-b2501e/TestDocs/tasks/traffic-management/egress/egress-gateway/test.sh/test.sh/_test_context/test.sh_output.txt

Goal

1. find and fix the issue with test framework
2. fix the test content/en/docs/tasks/traffic-management/egress/egress-gateway/test.sh mentioned in the description

References

relates to #14577

FYI @frankbu