Always let Dependabot propose Cargo.lock updates

[Eliah Kagan (EliahKagan)]

This fixes a bug in the dependabot.yml configuration since #1948, where we intend Dependabot to include the effect of cargo update, but this does not happen because dependency-type: all was not explicitly allowed.

This does not make an analogous change to the Dependabot configuration for GitHub Actions, because all and direct currently have the same effect for them (and it is not obvious how it would work if that ever changes, or which we would prefer).

For details on why this is needed for Dependabot to update most locked dependencies in Cargo.lock aside from the case where the update is done as part of updating a Cargo.toml dependency, see:

• https://docs.github.com/en/code-security/dependabot/dependabot-version-updates/controlling-dependencies-updated#allowing-specific-dependencies-to-be-updated
• https://docs.github.com/en/code-security/dependabot/working-with-dependabot/dependabot-options-reference#dependency-type-allow

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This does not change the cadence, which is still set to monthly. Dependabot will perform a check after this is merged, because any change to dependabot.yml triggers new Dependabot version update checks for all configured ecosystems. It will open a PR because there will be updates, most but not all of which will be changes to Cargo.lock updating transitive dependencies that were not covered before due to the configuration shortcoming that this is fixing.

The fork-internal Dependabot test PR I used to verify these changes, formed by pushing this change to main in my fork and subsequently rewinding, was EliahKagan#22. This roughly reflects what the first Dependabot PR after this configuration change is merged will look like.

I will make a corresponding change to dependabot.yml in cargo-smart-release, where GitoxideLabs/cargo-smart-release#52 had the same bug as #1948. (Edit: This change is GitoxideLabs/cargo-smart-release#58.)

No such change in prodash is needed. This is because Dependabot version updates are only used for GitHub Actions, not for Rust/cargo dependencies, and also because we are not currently committing Cargo.lock in prodash.

The problem this is fixing does not affect the behavior of Dependabot security updates, which are already attempted for all types of dependencies.

[Eliah Kagan (EliahKagan)]

The failure is due to #1816 and not related to any changes in this PR. I will rerun the workflow.