Bump vendor/github.com/cloudflare/boringtun from f672bb6 to 64a2fc7

Bumps [vendor/github.com/cloudflare/boringtun](https://github.com/cloudflare/boringtun) from `f672bb6` to `64a2fc7`.
- [Release notes](https://github.com/cloudflare/boringtun/releases)
- [Commits](cloudflare/boringtun@f672bb6...64a2fc7)

---
updated-dependencies:
- dependency-name: vendor/github.com/cloudflare/boringtun
  dependency-type: direct:production
...

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