Fixed some typos, courtesy of codespell

src/libstrongswan/credentials/credential_set.h

@@ -37,7 +37,7 @@ typedef struct credential_set_t credential_set_t;
  *
  * A credential set enumerator may not block the credential set, i.e. multiple
  * threads must be able to hold multiple enumerators, as the credential manager
- * is higly parallelized. The best way to achieve this is by using shared
+ * is highly parallelized. The best way to achieve this is by using shared
  * read locks for the enumerators only. Otherwise deadlocks will occur.
  * The writing cache_cert() routine is called by the manager only if no
  * enumerator is alive, so it is save to use a write lock there.