Bootstrap git submodule v4.5.3, not in sync with partials/scripts.html (still v4.6.0)

[pschrey2]

Discussed in #631

^{Originally posted by pschrey2 July 13, 2021}
Hi, bootstrap seems to be switched back to version 4.5.3 on May 29 with commit c5f1613 (see git submodule bootstrap at https://github.com/google/docsy/tree/master/assets/vendor).
Any reason for that?
Regards, Patrik

Happened by mistake during PR #554. Can the /assets/vendor/bootstrap git submodule be refered back to version 4.6.0?
Because now the submodule and https://github.com/google/docsy/blob/master/layouts/partials/scripts.html are not in sync.

The upgrade was done earlier by @deining on April 12 (8b2f695#diff-05e01d0fe33a568f907cb8c03ee25e8cef7221d73f052ac04392232753d25467) plus an SRI hash fix later on April 17.

[LisaFC]

Done! (also I hate updating git submodules, it always feels like bomb disposal)