[rubygems/rubygems] Use OpenSSL constants for error codes.

This fixes the following test error testing against OpenSSL 3.x:

~~~
  2) Failure:
TestGemRequest#test_verify_certificate_extra_message [/builddir/build/BUILD/ruby-3.0.2/test/rubygems/test_gem_request.rb:358]:
<"ERROR:  SSL verification error at depth 0: invalid CA certificate (24)\n" +
"ERROR:  Certificate  is an invalid CA certificate\n"> expected but was
<"ERROR:  SSL verification error at depth 0: invalid CA certificate (79)\n" +
"ERROR:  Certificate  is an invalid CA certificate\n">.
~~~

Where the root cause is this OpenSSL commit:

openssl/openssl@1e41dad

It seems that OpenSSL upstream considers the constant value just an
implementation detail and therefore this changes the test case to
follow the suite.

rubygems/rubygems@8acf8e95dc

test/rubygems/test_gem_request.rb

@@ -354,30 +354,36 @@ def test_user_agent_revision_missing
 
   def test_verify_certificate
     pend if Gem.java_platform?
+
+    error_number = OpenSSL::X509::V_ERR_OUT_OF_MEM
+
     store = OpenSSL::X509::Store.new
     context = OpenSSL::X509::StoreContext.new store
-    context.error = OpenSSL::X509::V_ERR_OUT_OF_MEM
+    context.error = error_number
 
     use_ui @ui do
       Gem::Request.verify_certificate context
     end
 
-    assert_equal "ERROR:  SSL verification error at depth 0: out of memory (17)\n",
+    assert_equal "ERROR:  SSL verification error at depth 0: out of memory (#{error_number})\n",
                  @ui.error
   end
 
   def test_verify_certificate_extra_message
     pend if Gem.java_platform?
+
+    error_number = OpenSSL::X509::V_ERR_INVALID_CA
+
     store = OpenSSL::X509::Store.new
     context = OpenSSL::X509::StoreContext.new store
-    context.error = OpenSSL::X509::V_ERR_INVALID_CA
+    context.error = error_number
 
     use_ui @ui do
       Gem::Request.verify_certificate context
     end
 
     expected = <<-ERROR
-ERROR:  SSL verification error at depth 0: invalid CA certificate (24)
+ERROR:  SSL verification error at depth 0: invalid CA certificate (#{error_number})
 ERROR:  Certificate  is an invalid CA certificate
     ERROR