Fix/850 testcontainers2 migration only springboot4

[Thomas-Iapichino]

What's changed?

• This PR reverts the changes from PR Upgrade testcontainers for the JUnit 5 migration #833 that caused the JUnit4to5Migration recipe to automatically trigger Testcontainers 2 migration for all Spring Boot upgrades.

Changes:

• Reverted ExcludeJUnit4UnlessUsingTestcontainers recipe precondition to check for org.testcontainers:*:1.x instead of spring-boot-testcontainers
• Removed Testcontainers2Migration from the ExcludeJUnit4UnlessUsingTestcontainers recipe list
• Updated test expectations to verify no changes occur when Testcontainers 1.x is present
• Added issue Spring Boot upgrades (any version) now causes upgrade to Testcontainers 2 #850 reference to affected tests

What's your motivation?

• Fixes Spring Boot upgrades (any version) now causes upgrade to Testcontainers 2 #850

• PR Upgrade testcontainers for the JUnit 5 migration #833 introduced a bug where upgrading Spring Boot (2.x or 3.x) would unintentionally trigger Testcontainers 2 migration. Since Spring Boot manages Testcontainers versions, this migration should only happen explicitly with Spring Boot 4 upgrades, not automatically during JUnit 4→5 migrations.

Anything in particular you'd like reviewers to focus on?

• The precondition now checks for org.testcontainers:*:1.x specifically. This ensures that:
  • Projects using Testcontainers 1.x keep JUnit 4 (as TC 1.x needs it)
  • Projects using Testcontainers 2.x can still exclude JUnit 4
  • Projects without Testcontainers can exclude JUnit 4

Anyone you would like to review specifically?

• @timtebeek (author of PR Upgrade testcontainers for the JUnit 5 migration #833)

Have you considered any alternatives or workarounds?

Any additional context

Checklist

• I've added unit tests to cover both positive and negative cases
• I've read and applied the recipe conventions and best practices
• I've used the IntelliJ IDEA auto-formatter on affected files