Python: Fix typo in change note

Author: hvitved

python/ql/src/change-notes/2021-12-17-add-SSRF-queries.md

@@ -1,4 +1,4 @@
 ---
-catgegory: newQuery
+category: newQuery
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 * Two new queries have been added for detecting Server-side request forgery (SSRF). _Full server-side request forgery_ (`py/full-ssrf`) will only alert when the URL is fully user-controlled, and _Partial server-side request forgery_ (`py/partial-ssrf`) will alert when any part of the URL is user-controlled. Only `py/full-ssrf` will be run by default.