Touch up PR 354

.github/dependabot.yml

@@ -6,10 +6,4 @@ updates:
       interval: daily
     commit-message:
       prefix: ''
-    ignore:
-      # For test on MSRV.
-      - dependency-name: once_cell
-      - dependency-name: serde
-      - dependency-name: toml
-      - dependency-name: trybuild
     labels: []

.github/workflows/ci.yml

@@ -87,7 +87,6 @@ jobs:
       - run: cargo build --manifest-path tests/no-std/Cargo.toml --target thumbv6m-none-eabi
       - run: cargo build --manifest-path tests/rust-2015/Cargo.toml --target thumbv6m-none-eabi
       - run: cargo minimal-versions build --workspace --all-features --ignore-private
-        if: matrix.rust != '1.56'
 
   miri:
     runs-on: ubuntu-latest

Cargo.toml

@@ -35,12 +35,7 @@ pin-project-auxiliary-macro = { path = "tests/auxiliary/macro" }
 macrotest = "1.0.9"
 rustversion = "1"
 static_assertions = "1"
-trybuild = "=1.0.67"
-
-# For test on MSRV.
-once_cell = "=1.14"
-serde = "1.0.159"
-toml = "=0.5.9"
+trybuild = "1.0.67"
 
 [patch.crates-io]
 prettyplease = { git = "https://github.com/taiki-e/prettyplease.git", branch = "dev" } # lower MSRV