Build gerrit docker image from almalinux

Gerrit docker images are now based on almalinux rather than Centos.

Change-Id: I1d44fe5e0d313f7672d26c253818b45cc65ec6b1
diff --git a/gerrit/Dockerfile b/gerrit/Dockerfile
index 4497b3b..e5aac9d 100644
--- a/gerrit/Dockerfile
+++ b/gerrit/Dockerfile
@@ -1,4 +1,4 @@
-FROM gerritcodereview/gerrit:$GERRIT_VERSION.$GERRIT_PATCH-centos8
+FROM gerritcodereview/gerrit:$GERRIT_VERSION.$GERRIT_PATCH-almalinux8
 
 ARG withXRay=false