Update base64 requirement from 0.11.0 to 0.12.0 (#1009)

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](marshallpierce/rust-base64@v0.11.0...v0.12.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Cargo.toml

@@ -107,7 +107,7 @@ wasm-bindgen = "0.2.59"
 # Changes here must be reflected in `build.rs`
 [target.'cfg(all(target_arch = "wasm32", not(target_os="wasi"), not(cargo_web)))'.dev-dependencies]
 wasm-bindgen-test = "0.3.4"
-base64 = "0.11.0"
+base64 = "0.12.0"
 ssri = "5.0.0"
 
 [target.'cfg(target_os = "emscripten")'.dependencies]