Fix typo from `occured` to `occurred`

[BaseMax]

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Fix typo from occured to occurred

[owen-mc]

There are three files with usages of "occured". In one it is deliberate and another file is a stub (i.e. copied from external code, with method bodies removed), so it probably shouldn't be changed. Only the ones in javascript/ql/test/query-tests/Security/CWE-912/tst.js appears to be incorrect and should be fixed.