Bump submodules/privacy-reference-tests from a3acc21 to 6b7ad1e

Bumps [submodules/privacy-reference-tests](https://github.com/duckduckgo/privacy-reference-tests) from `a3acc21` to `6b7ad1e`.
- [Release notes](https://github.com/duckduckgo/privacy-reference-tests/releases)
- [Commits](duckduckgo/privacy-reference-tests@a3acc21...6b7ad1e)

---
updated-dependencies:
- dependency-name: submodules/privacy-reference-tests
  dependency-type: direct:production
...

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