Cloned from: https://pagure.io/freeipa/issue/9854

### Issue
After migrating 389-dirsrv database (BDB->LMDB) and upgrading from Fedora 41->42 I noticed a new error message  in various `ipa` commands (`ipa-healthcheck`, `ipa server-cert-fix`, ...). 

#### Steps to Reproduce
1. (unconfirmed, most likely cause: run BDB -> LMDB migration)
2. run various `ipa` commands that use dsinstance.py:get_server_cert_nickname

#### Actual behavior
Error message `Unable to find server cert nickname in /etc/dirsrv/slapd-my-instance/dse.ldif` in output

#### Expected behavior
Since the entry is present, no error should occur.

#### Version/Release/Distribution
```
$ rpm -q freeipa-server freeipa-client ipa-server ipa-client 389-ds-base pki-ca krb5-server
freeipa-server-4.12.2-14.fc42.x86_64
freeipa-client-4.12.2-14.fc42.x86_64
package ipa-server is not installed
package ipa-client is not installed
389-ds-base-3.1.3-2.fc42.x86_64
package pki-ca is not installed
krb5-server-1.21.3-6.fc42.x86_64
```

#### Additional info:
In `dse.ldif` I can see 
```
dn: cn=rsa,cn=encryption,cn=config
cn: RSA
createTimestamp: 20170812014705Z
creatorsName: cn=directory manager
modifiersName: cn=directory manager
modifyTimestamp: 20170812014705Z
nsSSLActivation: on
nsSSLPersonalitySSL: Server-Cert
nsSSLToken: internal (software)
objectClass: top
objectClass: nsEncryptionModule
```

However, `parser.parse_results().keys()` appears to be empty. This is because the case changed and the entries_dn filter in "GetEntryFromLDIF" is wrong. However LDAP is not case sensitive, so any case should be supported, and therefore this is a bug. Probably all keys should be converted to lower case as should all lookups to preserve case insensitivity.