CVE-2023-28320.md: typo fix

docs/CVE-2023-28320.md

@@ -20,7 +20,7 @@ INFO
 Most platforms and systems build libcurl to use the threaded resolver or with
 c-ares, neither of those suffer from this flaw. Most platforms that build with
 the synchronous resolver do not feature `alarm()` and `siglongjmp()` and
-therefor are not vulnerable either.
+therefore are not vulnerable either.
 
 Since `alarm()` uses signals, it is not advisable to use in a multi-threaded
 environment (signals and threads rarely mix very well) which reduces the risk