[fix](mtmv) Avoid mutating excluded trigger tables

[foxtail463]

What problem does this PR solve?

Problem Summary:

isMTMVPartitionSync adds followed PCT tables into the excluded trigger table set while checking partition sync. Some callers pass immutable sets, such as the force-consistent rewrite path using ImmutableSet.of(), so partitioned MTMVs can fail with UnsupportedOperationException before the sync check finishes. Copy the input set into a local mutable set before adding derived PCT tables, avoiding mutation of caller-owned state and supporting immutable inputs.

[hello-stephen]

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Please clearly describe your PR:

1. What problem was fixed (it's best to include specific error reporting information). How it was fixed.
2. Which behaviors were modified. What was the previous behavior, what is it now, why was it modified, and what possible impacts might there be.
3. What features were added. Why was this function added?
4. Which code was refactored and why was this part of the code refactored?
5. Which functions were optimized and what is the difference before and after the optimization?

[foxtail463]

run buildall