Bump Oj to v3.13.20 to fix illegal instruction errors

What does this MR do and why?

v3.13.19 was not enough to fix x86 compatibility on older processors because some SSE instructions were used by the compiler in other parts of the code base. https://github.com/ohler55/oj/pull/806 disables SSE 4.2 optimizations by default.

Diff: https://my.diffend.io/gems/oj/3.13.19/3.13.20

Relates to #368656 (closed)

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