This PR addresses Issue #52320 by introducing conditional logic in the Helm Chart to support both Git Sync v3 and v4 credential environment variable formats.

Background

In Git Sync:

• v3 expects: GIT_SYNC_USERNAME, GIT_SYNC_PASSWORD
• v4 expects: GITSYNC_USERNAME, GITSYNC_PASSWORD

Prior to this change, the Airflow Helm Chart rendered all four variables, regardless of which version of Git Sync was being used. This led to confusion and potential misconfigurations.

What this PR changes

• Added a helper function git_sync.env_credentials in _helpers.tpl
  to conditionally render environment variables for git-sync v3 (GIT_SYNC_*) and v4 (GITSYNC_*) based on image tag.

• Replaced hardcoded credential environment variable blocks in Helm templates
  with the new include-based helper for better maintainability and correctness.

• Added two new parameterized unit tests:

  • test_git_sync_credentials_env_vars (for pod-template-file)
  • test_scheduler_git_sync_env_vars (for scheduler-deployment)
    Both test the expected env vars for v3 and v4 using @pytest.mark.parametrize.

Motivation

Previously, git-sync credential environment variables were rendered unconditionally for both v3 and v4,
causing redundancy and potential YAML issues. Also, tests for those were hard to maintain and unclear
when failures occurred due to overlapping expectations.

Benefits

• Cleaner and version-specific environment variable rendering
• Deterministic and clear testing logic per version
• Easier to maintain or extend in the future (e.g. sshKey or knownHosts support)

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