Fix directly uploading using a MIME type synonym

When Content-Type is "application/x-gzip", request.content_type resolves to "application/gzip", because application/x-gzip is a synonym of application/gzip by default. This causes the acceptable_content? check in ActiveStorage::DiskController to fail, because the direct upload token contains application/x-gzip, which is not equal to application/gzip.

Fix by comparing the token content type with the request content type *and its synonyms*.

activestorage/app/controllers/active_storage/disk_controller.rb

@@ -57,6 +57,6 @@ def decode_verified_token
     end
 
     def acceptable_content?(token)
-      token[:content_type] == request.content_type && token[:content_length] == request.content_length
+      token[:content_type] == request.content_mime_type && token[:content_length] == request.content_length
     end
 end

activestorage/test/controllers/disk_controller_test.rb

@@ -50,6 +50,16 @@ class ActiveStorage::DiskControllerTest < ActionDispatch::IntegrationTest
     assert_not blob.service.exist?(blob.key)
   end
 
+  test "directly uploading blob with different but equivalent content type" do
+    data = "Something else entirely!"
+    blob = create_blob_before_direct_upload(
+      byte_size: data.size, checksum: Digest::MD5.base64digest(data), content_type: "application/x-gzip")
+
+    put blob.service_url_for_direct_upload, params: data, headers: { "Content-Type" => "application/x-gzip" }
+    assert_response :no_content
+    assert_equal data, blob.download
+  end
+
   test "directly uploading blob with mismatched content length" do
     data = "Something else entirely!"
     blob = create_blob_before_direct_upload byte_size: data.size - 1, checksum: Digest::MD5.base64digest(data)