Skip threaded cache test on Windows

The test_get_or_create test uses Thread.join which can hang on Windows,
causing CI tests to run indefinitely.

This test creates 30 threads to test concurrent cache access. On Windows
with certain Ruby versions (observed with 3.3.10), Thread.join appears
to hang or take an extremely long time.

Skip this test on Windows platforms (mingw, mswin, cygwin) to prevent
CI timeouts.

Author: suketa

test/duckdb_test/instance_cache_test.rb

@@ -12,6 +12,8 @@ def test_s_new
       end
 
       def test_get_or_create
+        skip 'Thread.join hangs on Windows' if RUBY_PLATFORM.match?(/mingw|mswin|cygwin/)
+        
         cache = DuckDB::InstanceCache.new
         path = 'test_shared_db.db'
         30.times do