bump MSRV to 1.63

That way it should compile with minimal versions.

Reason for this is the following:

````
error: package `cc v1.0.98` cannot be built because it requires rustc 1.63 or newer, while the currently active rustc version is 1.56.1
````

.github/workflows/main.yml

@@ -83,7 +83,7 @@ jobs:
         os: [windows-2022, macos-latest, ubuntu-latest]
     env:
       # If this is changed to pass tests, then set `rust-version` in `Cargo.toml` to the same version.
-      version: 1.56.1
+      version: 1.63.0
     steps:
       - uses: actions/checkout@v4
       - name: Install Rust (rustup)

Cargo.toml

@@ -5,7 +5,7 @@ version = "1.0.33"
 edition = "2018"
 license = "MIT OR Apache-2.0"
 readme = "README.md"
-rust-version = "1.56.1"
+rust-version = "1.63.0"
 keywords = ["gzip", "deflate", "zlib", "zlib-ng", "encoding"]
 categories = ["compression", "api-bindings"]
 repository = "https://github.com/rust-lang/flate2-rs"