test: Pin manifests to stable v1.2-branch

[yanniszark]

What this PR does / why we need it:
Fixes the e2e tests by pinning the kubeflow/manifests dependency to a stable branch.

Which issue(s) this PR fixes:
Fixes #1433

[k8s-ci-robot]

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[yanniszark]

/retest

[yanniszark]

/retest

[yanniszark]

@andreyvelich some seemingly unrelated tests are failing:
build-suggestion-optuna, build-file-metrics-collector, build-db-manager, build-katib-controller.
The logs are not very helpful.

INFO[0046] Running: [/bin/sh -c if [ "$(uname -m)" = "ppc64le" ] || [ "$(uname -m)" = "aarch64" ]; then     apk --update add gcc musl-dev  &&     go build -o goptuna-suggestion
 ./v1beta1;     else     go build -o goptuna-suggestion ./v1beta1;     fi]
go: cannot find main module, but found Gopkg.lock in /go/src/github.com/kubeflow/katib
        to create a module there, run:
        cd ../../.. && go mod init
error building image: error building stage: failed to execute command: waiting for process to exit: exit status 1

Have you seen this before?

[andreyvelich]

I will check it.
/retest

[aws-kf-ci-bot]

@yanniszark: The following test failed, say /retest to rerun all failed tests:

Test name	Commit	Details	Rerun command
kubeflow-katib-presubmit	9edff8d	link	/test kubeflow-katib-presubmit

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[andreyvelich]

It seems that we have to switch to go modules to fix these errors.
I submitted PR: #1438 to implement it.

I think we can close this PR, thank you for investigation @yanniszark !

[yanniszark]

@andreyvelich thanks for taking the time to fix CI :)
Seems like it was a quite involved fix.