Fix nginx buildpack PR automation to update integration test expectations

[ivanovac]

Summary

Fixes the automatic nginx version PR generation to also update integration test expectations and override buildpack fixture, preventing test failures in all nginx version update PRs.

Note: This PR previously included a pipeline change to add a passed constraint to the update job. That change has been removed because it doesn't solve the root cause of the multi-stack issue. The proper fix for that is in PR #608 (atomic commits).

Problem

All automatically generated nginx version update PRs (#392, #394, #389, #390, #384, #385, etc.) are failing integration tests with two types of errors:

1. Override test: "Expected an error, got nil" - deployment succeeds when it should fail
2. Version tests: Timeout waiting for version strings that don't match
3. Available versions test: Expects old version list

Root Cause:
The automation in tasks/update-buildpack-dependency/run.rb updates manifest.yml with new nginx versions and adjusts version_lines (mainline/stable), but doesn't update:

• Integration test file src/nginx/integration/default_test.go (hardcoded version strings)
• Override buildpack fixture fixtures/util/override_buildpack/override.yml (fake version for testing)

Example: When nginx 1.29.7 is added and mainline changes from 1.28.x to 1.29.x:

Tests still expect:

• mainline => 1.28.
• Available versions: mainline, stable, 1.28.x, 1.29.x
• Override fixture has 1.28.999

But buildpack outputs:

• mainline => 1.29.
• Available versions: mainline, stable, 1.26.x, 1.28.x, 1.29.x
• Override 1.28.999 doesn't match mainline 1.29.x, so override doesn't apply

Changes

Enhanced tasks/update-buildpack-dependency/run.rb with nginx-specific file updates:

1. Update Integration Test Expectations

Updates src/nginx/integration/default_test.go patterns:

• using mainline => X.Y. → Updated to current mainline version
• Requested nginx version: mainline => X.Y. → Updated to current mainline version
• stable => X.Y. → Updated to current stable version
• Available versions: ... → Recalculated from manifest dependencies

2. Update Override Buildpack Fixture

Updates fixtures/util/override_buildpack/override.yml to match current mainline:

• Extracts mainline version (e.g., 1.29.x)
• Generates fake version (e.g., 1.29.999)
• Updates version_lines.mainline in override.yml
• Updates nginx dependency version
• Updates URI to reference fake version
• Keeps SHA256 intentionally wrong (for testing validation)

The override test uses a fake version with wrong SHA256 to verify the buildpack properly validates checksums. If the fake version doesn't match the mainline version line, the override won't apply and the test passes when it should fail.

3. Follows Existing Patterns

Uses same file-editing pattern as JRuby Gemfile updates - stores files in a hash and commits them together.

Testing Plan

After this PR is merged:

1. Close all failing nginx version PRs
2. Trigger regeneration of nginx 1.29.7 PR (or manually create one)
3. Verify the new PR includes updates to:
   • ✅ manifest.yml
   • ✅ src/nginx/integration/default_test.go
   • ✅ fixtures/util/override_buildpack/override.yml
4. Verify all integration tests pass (including override test)
5. Regenerate remaining nginx version PRs

Related Issues

• nginx-buildpack#392, Fix failing task #394, remove slack #389, Remove specs #390, Remove pivotal tracker references. #384, Remove buildpacks-site pipelines #385, remove .NET Core 7 #377, buildpack pipeline: remove all pivnet stuff #382, Fix deploy key locations #396, Remove tasks pinning from cflinuxfs4 pipeline #395, Update to gcc-11 and use latest available python for fs3 #378 - All failing integration tests
• nginx-buildpack#397, Allow empty stack diff release notes section #398, retry for httpd dependency build pipeline #399 - Attempted manual fixes (closed, superseded by this automation fix)

Dependencies

Should be merged before regenerating nginx version PRs to ensure new PRs have correct test expectations.