delay when to shutdown the mtping adapter

[lionelvillard]

Proposed Changes

• Make sure not to stop the mtping adapter to close to the minute during a graceful shutdown.

Release Note

- 🐛 Fix bug
PingSource does not lose events anymore when being shutdown close to the minute

Docs

[lionelvillard]

/test pull-knative-eventing-conformance-tests
/test pull-knative-eventing-integration-tests

[knative-test-reporter-robot]

The following jobs failed:

Test name	Triggers	Retries
pull-knative-eventing-conformance-tests		0/3
pull-knative-eventing-integration-tests		0/3

Failed non-flaky tests preventing automatic retry of pull-knative-eventing-integration-tests:

test/e2e.TestPingSourceV1Beta1EventTypes
test/e2e.TestPingSourceV1Beta1
test/e2e.TestPingSourceV1Alpha2
test/e2e.TestTriggerDependencyAnnotation
test/e2e.TestPingSourceV1Alpha2EventTypes

[knative-metrics-robot]

The following is the coverage report on the affected files.
Say /test pull-knative-eventing-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/adapter/mtping/adapter.go	87.5%	60.9%	-26.6
pkg/adapter/mtping/context.go	Do not exist	100.0%

[matzew]

/lgtm
/approve

[knative-prow-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lionelvillard, matzew

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• OWNERS [lionelvillard,matzew]

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