Bump the timeout for MRI tests on Linux

* They have a high variance.

Author: eregon

ci.jsonnet

@@ -542,7 +542,7 @@ local composition_environment = utils.add_inclusion_tracking(part_definitions, "
 
       "ruby-test-specs-linux": linux_gate + $.run.test_unit_tck_specs + { timelimit: "35:00" },
       "ruby-test-fast-linux":  linux_gate + $.run.test_fast + { timelimit: "30:00" }, # To catch missing slow tags
-      "ruby-test-mri-linux":   linux_gate + $.run.test_mri + { timelimit: "25:00" },
+      "ruby-test-mri-linux":   linux_gate + $.run.test_mri + { timelimit: "30:00" },
       "ruby-test-integration": linux_gate + $.run.test_integration,
       "ruby-test-cexts-linux": linux_gate + $.use.gem_test_pack + $.run.test_cexts,
       "ruby-test-gems":        linux_gate + $.use.gem_test_pack + $.run.test_gems,