Prow with mesh mode does not test with Istio mesh profile

[nak3]

In what area(s)?

/area networking
/area test-and-release

What version of Knative?

• HEAD

Expected Behavior

• prow tests with istio-ci-mesh/istio.yaml profile instead of istio-ci-no-mesh/istio.yaml.

Actual Behavior

• prow mesh test does not use istio-ci-mesh/istio.yaml but istio-ci-no-mesh/istio.yaml.

Steps to Reproduce the Problem

• Please refer to any log in https://testgrid.k8s.io/r/knative-own-testgrid/serving#istio-latest-mesh
• For example, 1681462884011347968/build-log.txt, it runs:

+ ./test/presubmit-tests.sh --run-test './test/e2e-tests.sh --istio-version latest --mesh' --run-test './test/e2e-auto-tls-tests.sh --istio-version latest --mesh'

but it uses istio-ci-no-mesh profile.

Got NET_ISTIO_COMMIT from /home/prow/go/src/knative.dev/serving/third_party/istio-latest/net-istio.yaml: ae9f4ffa632ccc62be2022ab0b1e66983e5c62d6
--2023-07-19 00:46:35--  https://raw.githubusercontent.com/knative-sandbox/net-istio/ae9f4ffa632ccc62be2022ab0b1e66983e5c62d6/third_party/istio-latest/istio-ci-no-mesh/istio.yaml

[dprotaso]

Some backstory.

We changed our parsing logic because of #12788 - afterwards we only 'parse' the flags once.

But the second time the script is invoked we have export SOMEVAR=0 which is resetting some variables. In theory marking the vars as readonly should prevent that but this doesn't seem to work in child processes.

I think it may be simpler to just dedupe flags in our knative/hack script

[dprotaso]

/assign @dprotaso