make overrides file for RHEL; move s390utils-base override there

Let's move the override added in [1] to a new file dedicated to
overrides. This will make it easier for us to identify and focus
on overcoming the issues related to the override.

[1] 71313d8

common.yaml

@@ -298,9 +298,8 @@ packages-aarch64:
   - irqbalance
 
 packages-s390x:
-  # Required for IBM Secure Execution
-  # Pinned due to https://github.com/openshift/os/issues/1731
-  - s390utils-base-2.33.1-2.el9
+  # Required genprotimg for IBM Secure Execution
+  - s390utils-base
 
 remove-from-packages:
   - - filesystem

manifest-rhel-9.6.yaml

@@ -12,6 +12,7 @@ variables:
 # Include manifests common to all RHEL and CentOS Stream versions
 include:
   - common.yaml
+  - overrides-rhel-9.6.yaml
 
 repos:
   - rhel-9.6-baseos

overrides-rhel-9.6.yaml

@@ -0,0 +1,9 @@
+# This is a poor man's version of an override lockfile for rhel-9.6. When needed
+# we gather any overrides NEVRs here to keep them in one place. When not needed,
+# empty or comment out this file (except this comment).
+
+#packages:
+
+packages-s390x:
+  # https://github.com/openshift/os/issues/1731
+  - s390utils-base-2.33.1-2.el9