bump msrv to 1.60.0

package `windows-result v0.1.2` cannot be built because it requires rustc 1.60 or newer

.github/workflows/test.yml

@@ -24,9 +24,8 @@ jobs:
     name: Test (${{ matrix.toolchain }})
     strategy:
       matrix:
-        # run on stable and beta to ensure that tests won't break on the next version of the rust
-        # toolchain
-        toolchain: [stable, beta, 1.56.0]
+        # run on beta to ensure that tests won't break on the next version of the rust toolchain
+        toolchain: [stable, beta, 1.60.0]
     steps:
       - name: Checkout
         uses: actions/checkout@v4

Cargo.toml

@@ -9,7 +9,8 @@ license = "MIT"
 keywords = ["winapi", "abstractions", "crossterm", "windows", "screen_buffer"]
 exclude = ["target", "Cargo.lock"]
 readme = "README.md"
-edition = "2018"
+edition = "2021"
+rust-version = "1.60.0"
 
 [target.'cfg(windows)'.dependencies]
 winapi = { version =  "0.3.8", features = ["winbase", "consoleapi", "processenv", "handleapi", "synchapi", "impl-default"] }