Update base64 requirement from 0.13.1 to 0.20.0

Updates the requirements on [base64](https://github.com/marshallpierce/rust-base64) to permit the latest version.
- [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/compare/v0.13.1...v0.20.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

Cargo.toml

@@ -18,7 +18,7 @@ features = ["events", "tls"]
 
 [dependencies]
 async-stream = { version = "0.3.3", optional = true }
-base64 = "0.13.1"
+base64 = "0.20.0"
 bitflags = "1.3.2"
 futures-util = { version = "0.3.25", features = ["sink"] }
 rgb = { version = "0.8.34", default-features = false }