Update GitHub actions (#124)

Also get rid of some warnings.

.github/workflows/features.yml

@@ -10,9 +10,9 @@ jobs:
     strategy:
       fail-fast: false
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Fetch toolchain
-        uses: actions-rs/toolchain@v1
+        uses: dtolnay/rust-toolchain@v1
         with:
           profile: minimal
           toolchain: nightly

.github/workflows/minimal-versions.yml

@@ -10,9 +10,9 @@ jobs:
     strategy:
       fail-fast: false
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Fetch toolchain
-        uses: actions-rs/toolchain@v1
+        uses: dtolnay/rust-toolchain@v1
         with:
           profile: minimal
           toolchain: nightly

.github/workflows/msrv-build.yml

@@ -10,9 +10,9 @@ jobs:
     strategy:
       fail-fast: false
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Fetch toolchain
-        uses: actions-rs/toolchain@v1
+        uses: dtolnay/rust-toolchain@v1
         with:
           profile: minimal
           toolchain: 1.56.0

.github/workflows/presubmit.yml

@@ -15,11 +15,10 @@ jobs:
         toolchain: [stable, beta, nightly]
 
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v3
       - name: Fetch toolchain
-        uses: actions-rs/toolchain@v1
+        uses: dtolnay/rust-toolchain@v1
         with:
-          profile: minimal
           toolchain: ${{ matrix.toolchain }}
           components: rustfmt, clippy
           target: thumbv6m-none-eabi

Cargo.toml

@@ -3,3 +3,4 @@ members = ["metadata_checks", "num_enum", "num_enum_derive", "renamed_num_enum",
 # Exclude num_enum_derive because its useful doc comments import num_enum, which the crate doesn't do (because it would
 # cause a circular dependency), so the doc tests don't actually compile.
 default-members  = ["num_enum", "renamed_num_enum", "serde_example", "stress_tests"]
+resolver = "2"

num_enum_derive/src/parsing.rs

@@ -86,11 +86,11 @@ impl EnumInfo {
     }
 
     fn parse_attrs<Attrs: Iterator<Item = Attribute>>(
-        mut attrs: Attrs,
+        attrs: Attrs,
     ) -> Result<(Ident, Option<ErrorType>)> {
         let mut maybe_repr = None;
         let mut maybe_error_type = None;
-        while let Some(attr) = attrs.next() {
+        for attr in attrs {
             if let Meta::List(meta_list) = &attr.meta {
                 if let Some(ident) = meta_list.path.get_ident() {
                     if ident == "repr" {