[RELEASE-1.14] [Backport] Fix bug in cert manager config (#15434)

[skonto]

• Backports knative@cac5e63

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[skonto]

For release 1.15 we are going to do an update later.

[ReToCode]

/lgtm
/approve

[openshift-ci]

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[openshift-cherrypick-robot]

@skonto: cannot checkout release-vX.Y: error checking out "release-vX.Y": exit status 1 error: pathspec 'release-vX.Y' did not match any file(s) known to git

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• Backports knative@cac5e63

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