ci: use --feature-powerset --depth 2 in features check (#5007)

As has been pointed out a few times in the past (e.g., #4036 (comment)), each-feature 
is not sufficient for features check.

Ideally, we'd like to check all combinations of features, but there are too many
combinations. So limit the max number of simultaneous feature flags to 2 by --depth
option. I think this should be sufficient in most cases as @carllerche said in
taiki-e/cargo-hack#58.

.github/workflows/ci.yml

@@ -76,7 +76,7 @@ jobs:
         run: rustup update stable
       - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
-        run: cargo install cargo-hack
+        uses: taiki-e/install-action@cargo-hack
 
       # Run `tokio` with `full` features. This excludes testing utilities which
       # can alter the runtime behavior of Tokio.
@@ -279,14 +279,12 @@ jobs:
           override: true
       - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
-        run: cargo install cargo-hack
-      - name: check --each-feature
-        run: cargo hack check --all --each-feature -Z avoid-dev-deps
-      - name: check net,time
-        run: cargo check -p tokio --no-default-features --features net,time -Z avoid-dev-deps
+        uses: taiki-e/install-action@cargo-hack
+      - name: check --feature-powerset
+        run: cargo hack check --all --feature-powerset --depth 2 -Z avoid-dev-deps --keep-going
       # Try with unstable feature flags
-      - name: check --each-feature --unstable
-        run: cargo hack check --all --each-feature -Z avoid-dev-deps
+      - name: check --feature-powerset --unstable
+        run: cargo hack check --all --feature-powerset --depth 2 -Z avoid-dev-deps --keep-going
         env:
           RUSTFLAGS: --cfg tokio_unstable -Dwarnings
 
@@ -316,7 +314,7 @@ jobs:
           override: true
       - uses: Swatinem/rust-cache@v1
       - name: Install cargo-hack
-        run: cargo install cargo-hack
+        uses: taiki-e/install-action@cargo-hack
       - name: "check --all-features -Z minimal-versions"
         run: |
           # Remove dev-dependencies from Cargo.toml to prevent the next `cargo update`
@@ -501,13 +499,13 @@ jobs:
 
       # Install dependencies
       - name: Install cargo-hack
-        run: cargo install cargo-hack
+        uses: taiki-e/install-action@cargo-hack
 
       - name: Install wasm32-wasi target
         run: rustup target add wasm32-wasi
 
       - name: Install wasmtime
-        run: cargo install wasmtime-cli
+        uses: taiki-e/install-action@wasmtime
 
       - name: Install cargo-wasi
         run: cargo install cargo-wasi
@@ -557,4 +555,3 @@ jobs:
           cargo install cargo-check-external-types --locked --version 0.1.3
           cargo check-external-types --all-features --config external-types.toml
         working-directory: tokio
-