Update base64 requirement from 0.13.0 to 0.21.5

Updates the requirements on [base64](https://github.com/marshallpierce/rust-base64) to permit the latest version.
- [Changelog](https://github.com/marshallpierce/rust-base64/blob/master/RELEASE-NOTES.md)
- [Commits](marshallpierce/rust-base64@v0.13.0...v0.21.5)

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

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

crates/bevy_gltf/Cargo.toml

@@ -37,7 +37,7 @@ gltf = { version = "1.3.0", default-features = false, features = [
     "utils",
 ] }
 thiserror = "1.0"
-base64 = "0.13.0"
+base64 = "0.21.5"
 percent-encoding = "2.1"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1"