Fix .travis.yml to keep s390x-linux as allow_features

[Misc #16360]

.travis.yml

@@ -418,6 +418,7 @@ matrix:
     - <<: *arm64-linux
     - <<: *i686-linux
     - <<: *arm32-linux
+    - <<: *s390x-linux
     - <<: *pedanticism
     - <<: *assertions
     - <<: *baseruby
@@ -438,10 +439,10 @@ matrix:
     - <<: *CALL_THREADED_CODE
     - <<: *NO_THREADED_CODE
   allow_failures:
+    - name: s390x-linux
     - name: -fsanitize=address
     - name: -fsanitize=memory
     - name: -fsanitize=undefined
-    - <<: *s390x-linux
   fast_finish: true
 
 before_script: