Raise minimum tested compiler to 1.60

Required by byteorder dependency:

    error: package `byteorder v1.5.0` cannot be built because it
    requires rustc 1.60 or newer, while the currently active rustc
    version is 1.56.1

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable, 1.56.0]
+        rust: [nightly, beta, stable, 1.60.0]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v4