example: fix and update grafana version (#5203)

[ti-chi-bot]

This is an automated cherry-pick of #5203

What problem does this PR solve?

Close #4845

The tag of Grafna has no v prefix, like https://hub.docker.com/layers/grafana/grafana/7.5.11/images/sha256-c6d621725df5a179bb19f8fd3c8c7bd10fee915edc98a4418d0a21011e104f9b?context=explore

What is changed and how does it work?

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[ti-chi-bot]

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