Require rubypick only on Fedora

There is no rubypick in rhel/centos but is in Fedora:

7724c2d703/f/ruby.spec (_146-148)

This is the same fix as:

https://src.fedoraproject.org/fork/lzachar/tests/ruby/c/98bf2ce800d42d3b17df5af62b782c43d39f21f3

systemtap-static-probes-in-ruby/main.fmf

@@ -1,3 +1,10 @@
+adjust:
+- when: distro != fedora
+  require-:
+  - rubypick
+  environment:
+    PACKAGES: "ruby rubygems"
+
 summary: It tests there are static probes in ruby package.
 description: |
     Simple test to exercise ruby's systemtap API.