Update bundled cJSON to version 1.7.18
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This merge request is automatically cherrypicked from !1796 (merged) from source branch https://source.coderefinery.org/ellert/arc/-/tree/update-cjson orginally made by @ellert .
The original MR went to branch: https://source.coderefinery.org/nordugrid/arc/-/tree/master
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Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1076549