Fix duplicate environment variables in MergeEnvVars

[Shubbu03]

Changes

Fix env.MergeEnvVars so duplicate environment variable names within the incoming slice are detected correctly.

When overwriting is disabled, duplicates now return an error. When enabled, the latest value replaces the earlier one while preserving order. Validation also runs when the destination slice is empty.

Added regression tests for duplicate values, ValueFrom, empty destinations, ordering, and forbidden variables.

Related Issue

Fixes #2330

Type of PR

/kind bug

Submitter Checklist

• Includes tests if functionality changed/was added
• Includes docs if changes are user-facing
• Kind label has been set
• Release notes block has been filled in, or marked NONE

Release Notes

Fixed duplicate environment variable handling in env.MergeEnvVars, preventing duplicate variables from appearing in generated build execution resources.

[openshift-ci]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by:
Once this PR has been reviewed and has the lgtm label, please assign qu1queee for approval. For more information see the Code Review Process.

The full list of commands accepted by this bot can be found here.

Details

Needs approval from an approver in each of these files:

• OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[kaizakin]

@Shubbu03 please sign your commits

also please check the release note against the template

[Shubbu03]

Thanks @kaizakin — both items should be addressed now:

• The commit is signed off.
• The release-note block is also fixed.

[kaizakin]

/ok-to-test

[kaizakin]

we have to do some dedup check for into as well
because as of now suppose from is empty, function returns in the first if check without considering whether into has duplicates

even if the control moves down, constructing a map with into alone overwrites the env variable considering it has duplicates (which we shouldn't do if the overwritevalues is set to false)