ci: Fix perf jobs blocking Marge pipelines.

They got accidentally disabled entirely, so they didn't block merge, but
once they re-enable then they'll block us again.  The problem was that I
moved allow_failure to a .performance-rules section, but we only ever
inherit the rules from that location, not the rest of yml.

This is basically a revert of 67547a04b6 ("ci: Move the performance
jobs' allow_failure:true to the gl rules."), though I still keep the
allow_failure in a more common location with comments, since perf jobs are
a huge trap.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21002>

.gitlab-ci/test-source-dep.yml

@@ -329,6 +329,7 @@
   rules:
     - !reference [.performance-rules, rules]
     - !reference [.freedreno-manual-rules, rules]
+  allow_failure: true # see comment in .performance-rules, which we don't inherit this line from.
 
 .nouveau-rules:
   stage: nouveau
@@ -547,6 +548,7 @@
     - changes:
         *virgl_file_list
       when: manual
+  allow_failure: true # see comment in .performance-rules, which we don't inherit this line from.
 
 .venus-rules:
   stage: layered-backends
@@ -667,6 +669,7 @@
     - changes:
         *iris_file_list
       when: manual
+  allow_failure: true # see comment in .performance-rules, which we don't inherit this line from.
 
 .anv-rules:
   stage: intel