Bump cel-go to v0.17.8 to pick up CEL estimated cost fix

[jpbetz]

What type of PR is this?

/kind bug

What this PR does / why we need it:

Picks up fix for google/cel-go#901

Special notes for your reviewer:

This is a somewhat rare edge case. I'd like to treat this as a bug and fix it and backport it.

Does this PR introduce a user-facing change?

Fix CEL estimated cost to for expressions that perform operations on the result of `map()` 
operations, (e.g. `.map(...).exists(...)` ) to have the correct estimated instead of an unbounded 
cost.

[liggitt]

/lgtm
/approve
/retest

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jpbetz, liggitt

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[k8s-ci-robot]

LGTM label has been added.

Git tree hash: d54e9b9aaa368fb782ca3c73c572aa1562e591f9

[k8s-ci-robot]

@jpbetz: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-kubernetes-e2e-gce-providerless	31f7efa	link	false	/test pull-kubernetes-e2e-gce-providerless

Full PR test history. Your PR dashboard. Please help us cut down on flakes by linking to an open issue when you hit one in your PR.

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