Bump base64 from 0.13.0 to 0.21.0 in /src/agent

Bumps [base64](https://github.com/marshallpierce/rust-base64) from 0.13.0 to 0.21.0.
- [Release notes](https://github.com/marshallpierce/rust-base64/releases)
- [Changelog](https://github.com/marshallpierce/rust-base64/blob/master/RELEASE-NOTES.md)
- [Commits](marshallpierce/rust-base64@v0.13.0...v0.21.0)

---
updated-dependencies:
- dependency-name: base64
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

src/agent/Cargo.lock

@@ -9,7 +9,7 @@ license = "MIT"
 [dependencies]
 anyhow = "1.0"
 async-trait = "0.1"
-base64 = "0.13"
+base64 = "0.21"
 bytes = "1.4"
 dunce = "1.0"
 dynamic-library = { path = "../dynamic-library" }

src/agent/onefuzz/Cargo.toml

@@ -9,7 +9,7 @@ license = "MIT"
 anyhow = "1.0"
 async-trait = "0.1"
 backoff = { version = "0.4", features = ["tokio"] }
-base64 = "0.13"
+base64 = "0.21"
 bytes = { version = "1.4", features = ["serde"] }
 derivative = "2.2"
 flume = "0.10"