executor/simple: prohibit setting a resource group to a role (#54525)

[ti-chi-bot]

This is an automated cherry-pick of #54525

What problem does this PR solve?

Issue Number: close #54417, ref #54434.

What changed and how does it work?

Check if a user is a role before assigning a resource group to it.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[codecov]

Codecov Report

Attention: Patch coverage is 33.33333% with 18 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.1@b90e57a). Learn more about missing BASE report.

Additional details and impacted files

@@               Coverage Diff                @@
##             release-8.1     #54551   +/-   ##
================================================
  Coverage               ?   71.3051%           
================================================
  Files                  ?       1465           
  Lines                  ?     422281           
  Branches               ?          0           
================================================
  Hits                   ?     301108           
  Misses                 ?     100750           
  Partials               ?      20423           

Flag	Coverage Δ
unit	71.3051% <33.3333%> (?)

Flags with carried forward coverage won't be shown. Click here to find out more.

Components	Coverage Δ
dumpling	53.9957% <0.0000%> (?)
parser	∅ <0.0000%> (?)
br	41.0456% <0.0000%> (?)

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-07-10 09:47:43.345913809 +0000 UTC m=+437360.581147922: ☑️ agreed by JmPotato.
• 2024-07-11 02:16:54.34487841 +0000 UTC m=+496711.580112523: ☑️ agreed by nolouch.

[nolouch]

/retest-required

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JmPotato, nolouch, tangenta

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[JmPotato]

/test build

[tiprow]

@JmPotato: No presubmit jobs available for pingcap/tidb@release-8.1

In response to this:

/test build

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