fix: ignore deprecation warnings for bootstrap v5

[abutterworth]

Eliminate this noise from builds:

WARNING: The `form-control-focus()` mixin has been deprecated as of v4.4.0. It will be removed entirely in v5.
         on line 8 of node_modules/bootstrap/scss/mixins/_deprecate.scss, in mixin `deprecate`
         from line 26 of node_modules/bootstrap/scss/mixins/_forms.scss, in mixin `form-control-focus`
         from line 15 of node_modules/@edx/paragon/src/Fieldset/Fieldset.scss
         from line 3 of node_modules/@edx/paragon/src/index.scss
         from line 1 of node_modules/@edx/paragon/scss/core/_components.scss
         from line 45 of node_modules/@edx/paragon/scss/core/core.scss
         from line 2 of src/sass/base/_paragon.scss
         from line 4 of stdin
WARNING: The `bg-variant` mixin has been deprecated as of v4.4.0. It will be removed entirely in v5.
         on line 8 of node_modules/bootstrap/scss/mixins/_deprecate.scss, in mixin `deprecate`
         from line 15 of node_modules/bootstrap/scss/mixins/_background-variant.scss, in mixin `bg-variant`
         from line 6 of node_modules/@edx/paragon/scss/core/extensions/_utilities.scss
         from line 2 of node_modules/@edx/paragon/scss/core/_extensions.scss
         from line 46 of node_modules/@edx/paragon/scss/core/core.scss
         from line 2 of src/sass/base/_paragon.scss
         from line 4 of stdin
WARNING: `text-emphasis-variant()` has been deprecated as of v4.4.0. It will be removed entirely in v5.
         on line 8 of node_modules/bootstrap/scss/mixins/_deprecate.scss, in mixin `deprecate`
         from line 16 of node_modules/bootstrap/scss/mixins/_text-emphasis.scss, in mixin `text-emphasis-variant`
         from line 7 of node_modules/@edx/paragon/scss/core/extensions/_utilities.scss
         from line 2 of node_modules/@edx/paragon/scss/core/_extensions.scss
         from line 46 of node_modules/@edx/paragon/scss/core/core.scss
         from line 2 of src/sass/base/_paragon.scss
         from line 4 of stdin

[coveralls]

Coverage remained the same at 87.963% when pulling 292c854 on abutterworth/ignore-deprecation-warnings into 3655ea1 on master.

[edx-semantic-release]

🎉 This PR is included in version 7.2.1 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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