*: upgrade go version to v1.25.6 to avoid security vulnerabilities (#1080)

[ti-chi-bot]

This is an automated cherry-pick of #1080

What problem does this PR solve?

Issue Number: close #1078

Problem Summary:

Target: `usr/bin/tiproxy` (gobinary) (7 vulnerabilities)
[MEDIUM] Risk Library:  golang.org/x/crypto  Installed: `v0.40.0`
[CVE-2025-47914](https://nvd.nist.gov/vuln/detail/CVE-2025-47914) - MEDIUM - Fixed: `0.45.0`
[CVE-2025-58181](https://nvd.nist.gov/vuln/detail/CVE-2025-58181) - MEDIUM - Fixed: `0.45.0`
[UNKNOWN] Risk Library:  stdlib  Installed: `v1.25.5`
[CVE-2025-61726](https://nvd.nist.gov/vuln/detail/CVE-2025-61726) - UNKNOWN - Fixed: `1.24.12, 1.25.6`
[CVE-2025-61728](https://nvd.nist.gov/vuln/detail/CVE-2025-61728) - UNKNOWN - Fixed: `1.24.12, 1.25.6`
[CVE-2025-61730](https://nvd.nist.gov/vuln/detail/CVE-2025-61730) - UNKNOWN - Fixed: `1.24.12, 1.25.6`

Target: `usr/bin/tiproxyctl` (gobinary) (3 vulnerabilities)
[UNKNOWN] Risk Library:  stdlib  Installed: `v1.25.5`
[CVE-2025-61726](https://nvd.nist.gov/vuln/detail/CVE-2025-61726) - UNKNOWN - Fixed: `1.24.12, 1.25.6`
[CVE-2025-61728](https://nvd.nist.gov/vuln/detail/CVE-2025-61728) - UNKNOWN - Fixed: `1.24.12, 1.25.6`
[CVE-2025-61730](https://nvd.nist.gov/vuln/detail/CVE-2025-61730) - UNKNOWN - Fixed: `1.24.12, 1.25.6`

What is changed and how it works:

• Upgrade go to v1.25.6
• Upgrade golang.org/x/crypto to latest
• Use go1.25.6 to compile golangci-lint

Check List

Tests

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

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

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

None

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
⚠️ Please upload report for BASE (release-nextgen-20251023@470d0ee). Learn more about missing BASE report.

Additional details and impacted files

@@                     Coverage Diff                     @@
##             release-nextgen-20251023    #1082   +/-   ##
===========================================================
  Coverage                            ?   66.11%           
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  Files                               ?      137           
  Lines                               ?    13691           
  Branches                            ?        0           
===========================================================
  Hits                                ?     9052           
  Misses                              ?     4038           
  Partials                            ?      601           

Flag	Coverage Δ
unit	66.11% <ø> (?)

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[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: djshow832

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• OWNERS [djshow832]

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-02-09 03:29:12.662515835 +0000 UTC m=+155568.356655675: ☑️ agreed by djshow832.