apache: Update to 2.4.51

apache: Update to 2.4.51

For details see (2.49):
https://dlcdn.apache.org//httpd/CHANGES_2.4.49

For 2.51:
https://dlcdn.apache.org//httpd/CHANGES_2.4.51

"SECURITY: CVE-2021-42013: Path Traversal and Remote Code
Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete
fix of CVE-2021-41773) (cve.mitre.org)
It was found that the fix for CVE-2021-41773 in Apache HTTP
Server 2.4.50 was insufficient..."

Signed-off-by: Matthias Fischer <matthias.fischer@ipfire.org>
Reviewed-by: Adolf Belka <adolf.belka@ipfire.org>
Reviewed-by: Michael Tremer <michael.tremer@ipfire.org>
Signed-off-by: Arne Fitzenreiter <arne_f@ipfire.org>