perf(assets-retry): reduce nullish coalescing operator

[chenjiahan]

Summary

The nullish coalescing operator is very useful in modern JS code, but it generates some extra code when it is transpiled to ES5.

This PR uses || to replace ?? because they are equivalent in the assets retry runtime code.

• initialChunkRetry.min.js: 3,980 bytes -> 3,946 bytes
• asyncChunkRetry.min.js: 3,778 bytes -> 3,575 byte

Checklist

• Tests updated (or not required).
• Documentation updated (or not required).

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