CI: attempt to fix nightly builds in next branch

[BastiDood]

The Problem

Currently, the next branch's nightly builds fail due to its inability to compile the dashmap crate. According to the GitHub Actions logs, it turns out that this is due to xacrimon/dashmap#133, where it was discovered that serde unexpectedly introduced a semver-breaking change in a patch release. A patch was quickly issued for [email protected].

Now, this alone should fix the issue. Though, I would later find out while investigating the logs that dashmap had been pinned to 4.0.0. Looking at the Cargo.toml, Cargo should have pulled in the latest patch of dashmap (see the dependency declaration below).

serenity/Cargo.toml

Lines 155 to 158 in 7e0b1d3

	[dependencies.dashmap]
	version = "4"
	features = ["serde"]
	optional = true

Indeed, this is the case except for nightly builds. I went through the Git blames and found that #1222 made it so that the nightly builds only pulled in the "minimal version" of dependencies. Details of this nightly feature may be found at rust-lang/cargo#4100. Attached below is the workflow configuration in question:

serenity/.github/workflows/ci.yml

Line 93 in 7e0b1d3

run: cargo clean; cargo update -Z minimal-versions; cargo check

In effect, the invocation to cargo update -Z minimal-versions must have pinned dashmap to the buggy 4.0.0, hence the compilation failures.

Possible Courses of Action

1. Manually bump up the dependency declarations. This is the approach I took with this PR, which also happens to be the most conservative.
2. Explicitly use patch-only semver ranges for all dependencies via tilde requirements.
3. Revert the invocation to cargo update -Z minimal-versions so that CI will always pull in the latest semver-compatible dependencies.

[BastiDood]

Nice! It seems that the nightly builds now compile. The other checks seem to fail due to an error with the ring crate (which is a transitive dependency). Perhaps this can be investigated on another day. For now, the nightly builds have finally been fixed! 🎉