filter (ticdc): fix synpoint table is replicated in BDR mode (#10587)

[ti-chi-bot]

This is an automated cherry-pick of #10587

What problem does this PR solve?

Issue Number: close #10576

What is changed and how it works?

Make isSysSchema() also treat tidb_cdc as a system schema.
This also helps the case of non-BDR "A→B→C" scenario, where the syncpoint table of A→B polluted B→C.
When the schema tidb_cdc is considered as a system schema, it will not be listened to by CDC at all.

Check List

Tests

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

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Fix a bug that causes syncpoint table being replicated by cdc.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: asddongmen

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