sass-converter pinned to 1.78.0 until Bootstrap 5.5 is released

[gonX]

Workaround added in #266 but blocks update of sass-converter until Bootstrap 5.5

Originally posted by @gonX in #212

Upstream documentation: https://github.com/orgs/twbs/discussions/41370

• When this is solved, dependabot updates for sass-embedded should be reenabled by reopening build(deps): bump sass-embedded from 1.78.0 to 1.94.2 in /site #318