sessionctx: fix the value of analyze_version when upgrading 4.x to 5.… (#30743)

[ti-srebot]

cherry-pick #30743 to release-5.2
You can switch your code base to this Pull Request by using git-extras:

# In tidb repo:
git pr https://github.com/pingcap/tidb/pull/30752

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/tidb.git pr/30752:release-5.2-d660e483c2cf

---

What problem does this PR solve?

Issue Number: close #25422

Problem Summary:

Use the same way with #30650

What is changed and how it works?

When do upgrading, we first check whether the variable exists.
If not exist, we use the 1 which is the old behavior in 4.0 and before.

Check List

Tests

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

Documentation

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

Release note

Fix the unexpected value of `tidb_analyze_version` when upgrading from a version lower than 5.0

[ti-chi-bot]

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[ti-chi-bot]

@ti-srebot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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[ti-srebot]

/run-all-tests

[ti-srebot]

@winoros you're already a collaborator in bot's repo.

[VelocityLight]

This pull request is closed because it's related version has closed automatic cherry-picking.
If it's still needed, you can reopen it or just regenerate it using bot,
see:

• https://prow.tidb.io/command-help#cherrypick
• https://book.prow.tidb.net/#/plugins/cherrypicker

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• https://internals.tidb.io/t/topic/785