fix(toml): Don't require MSRV bump for pub/priv

In rust-lang#13308, we decided to make the feature gate for public/private
dependencies non-blocking.
Generally, people opt-in to a feature that is non-blocking through `-Z`
but some nightly users want an "always on" mode for this, so we offered
both in rust-lang#13340.
In rust-lang#13340, we made both feature gates work but we did not make them
non-blocking for stable, only nightly.

This change makes the feature gate non-blocking on stable.

src/cargo/util/toml/mod.rs

@@ -786,12 +786,8 @@ fn normalize_dependencies<'a>(
                 warnings,
             )?;
             if d.public.is_some() {
-                let public_feature = features.require(Feature::public_dependency());
-                let with_public_feature = public_feature.is_ok();
+                let with_public_feature = features.require(Feature::public_dependency()).is_ok();
                 let with_z_public = gctx.cli_unstable().public_dependency;
-                if !with_public_feature && (!with_z_public && !gctx.nightly_features_allowed) {
-                    public_feature?;
-                }
                 if matches!(kind, None) {
                     if !with_public_feature && !with_z_public {
                         d.public = None;

tests/testsuite/pub_priv.rs

@@ -226,7 +226,6 @@ fn pub_dev_dependency_without_feature() {
         .build();
 
     p.cargo("check --message-format=short")
-        .masquerade_as_nightly_cargo(&["public-dependency"])
         .with_stderr_data(str![[r#"
 [WARNING] 'public' specifier can only be used on regular dependencies, not dev-dependencies
 [UPDATING] `dummy-registry` index