Fix build error with -Z minimal-versions

```
error[E0635]: unknown feature `proc_macro_span_shrink`
  --> /home/runner/.cargo/registry/src/index.crates.io-6f17d22bba15001f/proc-macro2-1.0.52/src/lib.rs:92:30
   |
92 |     feature(proc_macro_span, proc_macro_span_shrink)
   |                              ^^^^^^^^^^^^^^^^^^^^^^
```

Author: taiki-e

.github/workflows/ci.yml

@@ -152,18 +152,17 @@ jobs:
       - run: cargo build --tests --features default,thread-pool,io-compat --manifest-path futures/Cargo.toml
 
   minimal-versions:
-    name: cargo build -Z minimal-versions
+    name: cargo minimal-versions build
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v3
       - name: Install Rust
         run: rustup update nightly && rustup default nightly
       - name: Install cargo-hack
         uses: taiki-e/install-action@cargo-hack
-      # remove dev-dependencies to avoid https://github.com/rust-lang/cargo/issues/4866
-      - run: cargo hack --remove-dev-deps --workspace
-      - run: cargo update -Z minimal-versions
-      - run: cargo build --workspace --all-features
+      - name: Install cargo-minimal-versions
+        uses: taiki-e/install-action@cargo-minimal-versions
+      - run: cargo minimal-versions build --workspace --ignore-private --all-features
 
   no-std:
     name: cargo build --target ${{ matrix.target }}

futures-macro/Cargo.toml

@@ -16,6 +16,6 @@ proc-macro = true
 [features]
 
 [dependencies]
-proc-macro2 = "1.0"
+proc-macro2 = "1.0.60"
 quote = "1.0"
 syn = { version = "2.0.8", features = ["full"] }