Replace === with regular === on SyscallError

Without this Trilogy::SyscallError::* matches all matching instances of
::Errno::*, which makes the subclass useless in differentiating.

Co-authored-by: Daniel Colson <composerinteralia@github.com>

contrib/ruby/lib/trilogy/error.rb

@@ -12,15 +12,18 @@ module ConnectionError
   end
 
   # Trilogy may raise various syscall errors, which we treat as Trilogy::Errors.
-  class SyscallError
+  module SyscallError
     ERRORS = {}
 
     Errno.constants
       .map { |c| Errno.const_get(c) }.uniq
       .select { |c| c.is_a?(Class) && c < SystemCallError }
       .each do |c|
         errno_name = c.to_s.split('::').last
-        ERRORS[c::Errno] = const_set(errno_name, Class.new(c) { include Trilogy::ConnectionError })
+        ERRORS[c::Errno] = const_set(errno_name, Class.new(c) {
+          include Trilogy::ConnectionError
+          singleton_class.define_method(:===, Module.instance_method(:===))
+        })
       end
 
     ERRORS.freeze

contrib/ruby/test/client_test.rb

@@ -1099,4 +1099,14 @@ def test_connection_options_casting
 
     assert client.query("SELECT 1")
   end
+
+  def test_error_classes_exclusively_match_subclasses
+    klass = Trilogy::SyscallError::ECONNRESET
+    assert_operator klass, :===, klass.new
+    refute_operator klass, :===, Errno::ECONNRESET.new
+
+    assert_operator Errno::ECONNRESET, :===, klass.new
+    assert_operator SystemCallError, :===, klass.new
+    assert_operator Trilogy::ConnectionError, :===, klass.new
+  end
 end