Clarify MMR historical dose sequence validation message

Make the validation error for invalid MMR historical dose sequence values
more consistent when uploading vaccination records.

Before this change, invalid values such as `3` and `2B` could show different
error messages. This change updates the wording so they now both show the
same message explaining that the dose sequence cannot be greater than 2.

This follows on from commit 9035a26.

Jira-Issue: MAV-2312

Author: jhenderson

app/models/immunisation_import_row.rb

@@ -851,13 +851,15 @@ def validate_dose_sequence
         two_words_connector: " or "
       )
 
+    dose_sequence_error_message =
+      "The dose sequence number cannot be greater than " \
+        "#{maximum_dose_sequence}. Enter a dose sequence number, " \
+        "for example, #{dose_sequence_examples}."
+
     if dose_sequence.present? ||
          parsed_vaccination_description_string&.dig(:dose_sequence).present?
       if dose_sequence_value.nil?
-        errors.add(
-          field.header,
-          "Enter a dose sequence number, for example, #{dose_sequence_examples}."
-        )
+        errors.add(field.header, dose_sequence_error_message)
       elsif maximum_dose_sequence
         if dose_sequence_value < 1
           errors.add(field.header, "must be greater than 0")
@@ -879,10 +881,7 @@ def validate_dose_sequence
           end
         )
       else
-        errors.add(
-          field.header,
-          "Enter a dose sequence number, for example, #{dose_sequence_examples}."
-        )
+        errors.add(field.header, dose_sequence_error_message)
       end
     end
   end

spec/models/immunisation_import_row_spec.rb

@@ -582,7 +582,7 @@
         it "has the correct error message" do
           immunisation_import_row.valid?
           expect(immunisation_import_row.errors["DOSE_SEQUENCE"]).to include(
-            "Enter a dose sequence number, for example, 1 or 2."
+            "The dose sequence number cannot be greater than 2. Enter a dose sequence number, for example, 1 or 2."
           )
         end
       end