Fix flaky TestSetTraceFunc#test_remove_in_trace by filtering trace events

Merged: https://github.com/ruby/ruby/pull/11368

test/ruby/test_settracefunc.rb

@@ -456,6 +456,9 @@ class TestSetTraceFunc < Test::Unit::TestCase
     bug3921 = '[ruby-dev:42350]'
     ok = false
     func = lambda{|e, f, l, i, b, k|
+      # In parallel testing, unexpected events like IO operations may be traced,
+      # so we filter out events here.
+      next unless f == __FILE__
       set_trace_func(nil)
       ok = eval("self", b)
     }