Bump website/themes/uswds from bc74e15 to ac7915f (#280)

Bumps [website/themes/uswds](https://github.com/usnistgov/hugo-uswds) from `bc74e15` to `ac7915f`.
- [Release notes](https://github.com/usnistgov/hugo-uswds/releases)
- [Commits](usnistgov/hugo-uswds@bc74e15...ac7915f)

---
updated-dependencies:
- dependency-name: website/themes/uswds
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>