Fixes #11929 - Strip whitespace from csv headers (#11956)

* Strip whitespace from csv headers

* Move strip() call to parse_csv()

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Co-authored-by: jeremystretch <jstretch@netboxlabs.com>

netbox/utilities/forms/utils.py

@@ -195,6 +195,7 @@ def parse_csv(reader):
     # `site.slug` header, to indicate the related site is being referenced by its slug.
 
     for header in next(reader):
+        header = header.strip()
         if '.' in header:
             field, to_field = header.split('.', 1)
             headers[field] = to_field