example: fix and update grafana version

[csuzhangxc]

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]

@dveeden: adding LGTM is restricted to approvers and reviewers in OWNERS files.

In response to this:

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: dveeden
Once this PR has been reviewed and has the lgtm label, please ask for approval from csuzhangxc. For more information see the Kubernetes Code Review Process.

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Needs approval from an approver in each of these files:

• OWNERS

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[codecov-commenter]

Codecov Report

Merging #5203 (134f518) into master (34c19d4) will decrease coverage by 0.03%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #5203      +/-   ##
==========================================
- Coverage   57.97%   57.95%   -0.03%     
==========================================
  Files         245      245              
  Lines       29240    29240              
==========================================
- Hits        16951    16945       -6     
- Misses      10641    10645       +4     
- Partials     1648     1650       +2     

Flag	Coverage Δ
unittest	57.95% <ø> (-0.03%)	⬇️

[csuzhangxc]

/cherry-pick release-1.5

[ti-chi-bot]

@csuzhangxc: The label(s) /release-1.5 cannot be applied, because the repository doesn't have them.

In response to this:

/cherry-pick release-1.5

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.

[ti-chi-bot]

@csuzhangxc: new pull request created to branch release-1.5: #5206.

In response to this:

/cherry-pick release-1.5

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the ti-community-infra/tichi repository.