chore(deps): bump base64 to 0.21.5

[cassie-rust]

Description of change

Bumps base64 version to 0.20.0, which contains breaking changes from 0.13.1

This PR only updates existing tests, which didn't compile with the upgrade.

I did not find any existing tests for url-unsafe characters, and I feel it's not my place to decide on the necessity of them -- I leave that to the maintainers to decide; there is a subtle difference in behavior, as explained here: marshallpierce/rust-base64#206 (comment)

Closes #1393

How has this been tested? (if applicable)

I ran cargo test -p shuttle-common before upgrade, and after. Both suites passed, which they shouldn't given the incompability. On trying to run the unit tests themselves, it failed, silently. Running the tests from vscode produces the following:

Executing task: cargo test --package shuttle-common --lib -- backends::auth::tests --nocapture 

    Finished test [unoptimized + debuginfo] target(s) in 0.22s
     Running unittests src/lib.rs (target/debug/deps/shuttle_common-28e6d65a277dfe89)

running 0 tests

test result: ok. 0 passed; 0 failed; 0 ignored; 0 measured; 9 filtered out; finished in 0.00s

I've yet to successfully even /run/ these tests, and I'm at my wit's end. However, cargo clippy will try and compile and blow up because of incompatibilities and so I used that as a guide. It compiles, but it has not been tested.

[orhun]

LGTM, thanks for your contribution!

[oddgrd]

Thanks @cassie-rust, this looks great! I'm wondering, should we upgrade to the latest version (currently 0.21.5)?

You'll need some feature flags enabled to run the tests: cargo test -p shuttle-common --features backend,service,display (or --all-features). They pass 🥳

[cassie-rust]

Sure, I can do that; it seems to mostly be namespace changes between 0.20 and 0.21

[oddgrd]

Cool!

[cassie-rust]

Bumped to 0.21.5 instead.

[jonaro00]

Thanks!