Bump base64 from 0.3.1 to 0.5.2 in /rust/template

Bumps [base64](https://github.com/marshallpierce/rust-base64) from 0.3.1 to 0.5.2.
- [Release notes](https://github.com/marshallpierce/rust-base64/releases)
- [Changelog](https://github.com/marshallpierce/rust-base64/blob/master/RELEASE-NOTES.md)
- [Commits](https://github.com/marshallpierce/rust-base64/commits/v0.5.2)

---
updated-dependencies:
- dependency-name: base64
  dependency-type: direct:production
...

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

Author: dependabot[bot]