[GR-20446] Roll back some removed entries in IO and StringIO MRI test excluded lists

Author: andrykonchin

test/mri/excludes/TestIO.rb

@@ -55,3 +55,4 @@
 exclude :test_advise_pipe, "needs investigation - fails on Linux"
 exclude :test_fcntl_lock_linux, "needs investigation - fails on Linux"
 exclude :test_select_memory_leak, "needs investigation"
+exclude :test_race_gets_and_close, "transient"

test/mri/excludes/TestStringIO.rb

@@ -17,6 +17,7 @@
 exclude :test_gets2, "needs investigation"
 exclude :test_gets_chomp, "needs investigation"
 exclude :test_gets_chomp_eol, "needs investigation"
+exclude :test_overflow, "needs investigation - it hangs up on darwin"
 exclude :"test_strip_bom:UTF-16BE", "needs investigation"
 exclude :"test_strip_bom:UTF-16LE", "needs investigation"
 exclude :"test_strip_bom:UTF-32BE", "needs investigation"