ddl: Fix sync empty schema diff

[JaySon-Huang]

What problem does this PR solve?

Issue Number: close #8578, close #8289

Problem Summary: When there is conflict in concurrency DDL, it will skip some schema version, which generate an empty SchemaDiff.

What is changed and how it works?

Skip when meets an empty SchemaDiff in the non-latest schema version
As that in the relese-7.1 branch #8578 (comment)

tiflash/dbms/src/TiDB/Schema/TiDBSchemaSyncer.h

Lines 233 to 262 in 9f7e054

	SchemaBuilder<Getter, NameMapper> builder(getter, context, databases, used_version);
	try
	{
	for (size_t diff_index = 0; diff_index < diffs.size(); ++diff_index)
	{
	const auto & schema_diff = diffs[diff_index];
	if (!schema_diff)
	{
	// If `schema diff` got empty `schema diff`(it's not the latest one, due to we check it before), we should just skip it.
	//
	// example:
	// - `cur_version` is 1, `latest_version` is 10
	// - The schema diff of schema version [2,4,6] is empty, Then we just skip it.
	// - The schema diff of schema version 10 is empty, Then we should just apply version into 9(which we check it before)
	LOG_WARNING(log, "Skip the schema diff from version {}. ", cur_version + diff_index + 1);
	continue;
	}
	if (schema_diff->regenerate_schema_map)
	{
	// If `schema_diff.regenerate_schema_map` == true, return `-1` direclty, let TiFlash reload schema info from TiKV.
	LOG_INFO(log, "Meets a schema diff with regenerate_schema_map flag");
	return -1;
	}
	builder.applyDiff(*schema_diff);
	}
	}

Refine the readme of running integration tests in local

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

Fix the crash issue after TiDB's concurrent DDL meets a conflict

[JaySon-Huang]

/run-all-tests

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JinheLin, Lloyd-Pottiger

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• OWNERS [JinheLin,Lloyd-Pottiger]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-12-29 01:45:27.194155499 +0000 UTC m=+1789418.231382423: ☑️ agreed by Lloyd-Pottiger.
• 2023-12-29 02:49:41.308491256 +0000 UTC m=+1793272.345718184: ☑️ agreed by JinheLin.

[JaySon-Huang]

/run-unit-test

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #8626.

[ti-chi-bot]

/cherry-pick release-7.5

[ti-chi-bot]

In response to a cherrypick label: new pull request could not be created: failed to create pull request against pingcap/tiflash#release-7.5 from head ti-chi-bot:cherry-pick-8623-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"No commits between pingcap:release-7.5 and ti-chi-bot:cherry-pick-8623-to-release-7.5"}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

[ti-chi-bot]

@ti-chi-bot: new pull request could not be created: failed to create pull request against pingcap/tiflash#release-7.5 from head ti-chi-bot:cherry-pick-8623-to-release-7.5: status code 422 not one of [201], body: {"message":"Validation Failed","errors":[{"resource":"PullRequest","code":"custom","message":"No commits between pingcap:release-7.5 and ti-chi-bot:cherry-pick-8623-to-release-7.5"}],"documentation_url":"https://docs.github.com/rest/pulls/pulls#create-a-pull-request"}

In response to this:

/cherry-pick release-7.5

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