Pin PHP 8.2 Bullseye package sources to Debian snapshot

[Saipriya-1144]

This PR pins the Debian Bullseye package sources used by the PHP 8.2 runtime, common base, and PHP SDK images to snapshot  20260831T211305Z ,

Bullseye reached end of life and packages referenced by the live repository are no longer consistently available. With this change, customer startup commands using apt-get update, apt-get install, or apt-get upgrade will use the frozen snapshot and avoid package download failures.

Old apt-sources file:

New apt-sources file:

• The purpose of this PR is explained in this message or in an issue. If an issue please include a reference as #<issue_number>.
• Tests are included and/or updated for code changes.
• Proper license headers are included in each file.

[github-actions]

SHA Validation Summary

Stack	Status
PHP	✅ success
.NET	✅ success

PHP Validation Output

Validating PHP SHA256 hashes from: images/constants.yml
==================================================
PHP 8.1.34: OK
PHP 8.2.33: OK
PHP 8.3.33: OK
PHP 8.4.25: OK
PHP 8.5.10: OK
==================================================
Validated: 5 PHP version(s)
SHA VALIDATION PASSED

.NET Validation Output

Validating .NET SHA512 hashes...
  .NET Runtime 8.0.31: OK
  .NET Runtime 9.0.20: OK
  NET_CORE_APP_100: SKIP (no SHA defined)
  NET_CORE_APP_110: SKIP (no SHA defined)
  ASP.NET Core 8.0.31: OK
  ASP.NET Core 9.0.20: OK
  ASPNET_CORE_APP_100: SKIP (no SHA defined)
  ASPNET_CORE_APP_110: SKIP (no SHA defined)
SHA VALIDATION PASSED