Restrict JUnit dependencies to below version 6.x to maintain compatib…

[ramanathan1504]

Related update for Fixes #4109

Add Dependabot ignore rules for JUnit 6+ updates

This PR updates .github/dependabot.yaml to prevent Dependabot from proposing JUnit 6 and above upgrades.

What changed

Added ignore rules for:

• org.junit:junit-bom with versions: [ "[6,)" ]
• org.junit.jupiter:* with versions: [ "[6,)" ]
• org.junit.platform:* with versions: [ "[6,)" ]
• org.junit.vintage:* with versions: [ "[6,)" ]

Applied for existing Maven update entries (2.x and main target branches).

How I tested

1. Triggered/ran Dependabot update after config change.
2. Reviewed the generated Dependabot PR(s), especially Files changed.
3. Checked dependency changes in pom.xml and related files.

Test result

• No JUnit dependency was upgraded to 6.x.
• Dependabot PR did not include JUnit 6+ bumps.
• This confirms the ignore rules are working as expected.

[ppkarwasz]

LGTM, thanks!