Merge r1923479 from trunk:

CI: Try to cope with CentOS Stream containers being out-of-sync with
the yum repos when building the slapd container. 



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1923480 13f79535-47bb-0310-9956-ffa450edef68

test/travis_Dockerfile_slapd.centos

@@ -1,5 +1,5 @@
 FROM quay.io/centos/centos:stream9
-RUN dnf install -y epel-release && \
-    dnf install -y openldap openldap-clients openldap-servers openldap-devel && \
-    dnf -y clean all --enablerepo='*'
+RUN rpm -q openldap-servers || (dnf install --refresh -y epel-release && \
+    dnf install --nobest -y openldap-clients openldap-servers openldap-devel && \
+    dnf -y clean all --enablerepo='*')
 CMD /usr/sbin/slapd -u ldap -d1 '-h ldap:// ldapi:///'