ci: Update minimum tested Rust version to 1.63

```
error: package `libc v0.2.167` cannot be built because it requires rustc 1.63 or newer, while the currently active rustc version is 1.61.0
```

Author: taiki-e

.github/workflows/ci.yml

@@ -35,9 +35,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - rust: '1.61'
+          - rust: '1.63'
             os: ubuntu-latest
-          - rust: '1.61'
+          - rust: '1.63'
             os: windows-latest
           - rust: stable
             os: ubuntu-latest