CI: switch to Fedora 38 build VM

Technically speaking this is unrelated to the way how we build the code
in the main CI (it doesn't matter how we build, say, `sysrepo-cpp` or
`velia` or `CzechLight/dependencies`), so let's make our life easier a
wee bit by migrating to a supported base OS.

Change-Id: I9c5f488141588468cd507cf1ae0e648084ccf1db
diff --git a/.zuul.yaml b/.zuul.yaml
index c33b12b..6386059 100644
--- a/.zuul.yaml
+++ b/.zuul.yaml
@@ -1,6 +1,6 @@
 - job:
     name: czechlight-clearfog
-    parent: run-ci-build-sh-f34
+    parent: run-ci-build-sh-f38
     timeout: 3600
     post-timeout: 600
     vars: