Bump MSRV due to syn 2

Author: oxalica

.github/workflows/ci.yaml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable, 1.49.0]
+        rust: [nightly, beta, stable, "1.56"]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v3

macros/Cargo.toml

@@ -8,7 +8,7 @@ categories = ["asynchronous", "network-programming", "development-tools::ffi"]
 license = "MIT"
 repository = "https://github.com/oxalica/async-ffi"
 readme = "../README.md"
-rust-version = "1.49" # Follows async-ffi
+rust-version = "1.56" # syn 2 requires edition 2021
 
 [lib]
 proc-macro = true