fix static scan warnings

app/main/views/send.py

@@ -4,6 +4,7 @@ import uuid
 from string import ascii_uppercase
 from zipfile import BadZipFile
 
+import bleach
 from flask import (
     abort,
     current_app,
@@ -170,7 +171,9 @@ def send_messages(service_id, template_id):
         error_message = '<span class="error-message usa-error-message">'
         error_message = f"{error_message}{first_field_errors[0]}"
         error_message = f"{error_message}</span>"
-        error_message = Markup(error_message)
+        # use 'nosec' because we applied bleach.clean to strip dangerous tags
+        error_message = bleach.clean(error_message)
+        error_message = Markup(error_message)  # nosec
         flash(error_message)
     column_headings = get_spreadsheet_column_headings_from_template(template)