Try skipping TupleSpaceProxyTest on MinGW UCRT64

As you all know, MinGW UCRT64 CI has randomly got stuck despite its
"Finished tests" output.

Looking at the logs closely, it seems like all of the recent such
reproductions end with the following output:

```
  Retrying hung up testcases...
  [ 1/14] Rinda::TupleSpaceProxyTest#test_ruby_talk_264062 = 0.21 s
  [ 2/14] Rinda::TupleSpaceProxyTest#test_00_template = 0.01 s
  [ 3/14] Rinda::TupleSpaceProxyTest#test_inp_rdp = 0.00 s
  [ 4/14] Rinda::TupleSpaceProxyTest#test_core_03_notify = 0.01 s
  [ 5/14] Rinda::TupleSpaceProxyTest#test_00_renewer = 0.01 s
  [ 6/14] Rinda::TupleSpaceProxyTest#test_cancel_02 = 0.11 s
  [ 7/14] Rinda::TupleSpaceProxyTest#test_00_DRbObject = 0.00 s
  [ 8/14] Rinda::TupleSpaceProxyTest#test_core_02 = 0.11 s
  [ 9/14] Rinda::TupleSpaceProxyTest#test_core_01 = 0.11 s
  [10/14] Rinda::TupleSpaceProxyTest#test_remote_array_and_hash = 0.01 s
  [11/14] Rinda::TupleSpaceProxyTest#test_00_tuple = 0.00 s
  [12/14] Rinda::TupleSpaceProxyTest#test_take_bug_8215 = 0.41 s
  [13/14] Rinda::TupleSpaceProxyTest#test_cancel_01 = 0.11 s
  [14/14] Rinda::TupleSpaceProxyTest#test_symbol_tuple = 0.01 s
  Finished tests in 719.252845s, 29.4292 tests/s, 3838.7154 assertions/s.
  21167 tests, 2761007 assertions, 0 failures, 0 errors, 708 skips
```

https://github.com/ruby/ruby/runs/7057789554

While it seems to be retried successfully, given that it hungs up once
and this appears all the time, this test class seems a bit suspicious.
To check if it's related, let me try disabling this for now.

test/rinda/test_rinda.rb

@@ -496,6 +496,9 @@ class TupleSpaceProxyTest < Test::Unit::TestCase
   include TupleSpaceTestModule
 
   def setup
+    if RUBY_PLATFORM.match?(/mingw/) && ENV['MSYSTEM'] == 'UCRT64'
+      omit 'This test seems to randomly hang on GitHub Actions MinGW UCRT64'
+    end
     super
     ThreadGroup.new.add(Thread.current)
     @ts_base = Rinda::TupleSpace.new(1)