fix(user_ldap): skip non-string elements from ldap_explode_dn in getDomainDNFromDN

[pk7243959-wq]

• Resolves: [Bug]: user_ldap: getDomainDNFromDN() includes count element from ldap_explode_dn(), producing invalid DN passed to ldap_read() #61446

Summary

ldap_explode_dn() returns an array containing a count key with an integer. In getDomainDNFromDN(), this integer was appended to $domainParts, resulting in an invalid DN syntax (e.g. dc=example,dc=com,4) passed to ldap_read().

This PR skips non-string elements in the loop so that getDomainDNFromDN() returns a valid domain DN.

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI