br: skip template system table __TiDB_BR_Temporary_mysql when backup (#41000)

[ti-chi-bot]

This is an automated cherry-pick of #41000

What problem does this PR solve?

Issue Number: close #40797

Problem Summary:
The process of br restore panic because of the duplicate template system table in __TiDB_BR_Temporary_mysql.

What is changed and how it works?

Skip template system table __TiDB_BR_Temporary_mysql when backup.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

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

Skip template system table __TiDB_BR_Temporary_mysql when backup.

[ti-chi-bot]

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