Bump MSRV to Rust 1.47

https://github.com/smol-rs/async-task/releases/tag/v4.3.0

.clippy.toml

@@ -1 +1 @@
-msrv = "1.40"
+msrv = "1.47"

.github/workflows/ci.yml

@@ -37,7 +37,7 @@ jobs:
       matrix:
         # When updating this, the reminder to update the minimum supported
         # Rust version in Cargo.toml and .clippy.toml.
-        rust: ['1.40']
+        rust: ['1.47']
     steps:
       - uses: actions/checkout@v3
       - name: Install Rust

Cargo.toml

@@ -6,7 +6,7 @@ name = "async-executor"
 version = "1.4.1"
 authors = ["Stjepan Glavina <stjepang@gmail.com>"]
 edition = "2018"
-rust-version = "1.40"
+rust-version = "1.47"
 description = "Async executor"
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/smol-rs/async-executor"