chore: to use clang-format 12 for tiflash version less than v7.4

[purelind]

for version <= 7.4, need use clang-format 12

[ti-chi-bot]

I have already done a preliminary review for you, and I hope to help you do a better job.

Based on the pull request, the key changes include:

• Adding a new stage called "clang-format-12" to the pull_integration_test.groovy file.
• Copying the clang-format-12 file to /usr/local/bin/clang-format and making it executable.
• This change is applicable for the Tiflash version less than or equal to 7.4.

There are no apparent potential problems with this pull request. However, it is recommended to consider the following suggestions:

• It is always a good practice to provide more detailed information in the pull request description, such as the reason behind the change and the expected outcome.
• It may be useful to add a check to ensure that the Tiflash version is less than or equal to 7.4 before running the "clang-format-12" stage.
• It may be helpful to add a comment in the code to explain the purpose of the "clang-format-12" stage.

Overall, the changes seem justified and should not cause any issues.

[ti-chi-bot]

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