Raise minimum tested compiler to 1.70

Required by clap 4.4.0.

    error: package `clap v4.4.0` cannot be built because it requires rustc
    1.70.0 or newer, while the currently active rustc version is 1.65.0
    Either upgrade to rustc 1.70.0 or newer, or use
    cargo update -p clap@4.4.0 --precise ver
    where `ver` is the latest version of `clap` supporting rustc 1.65.0

.github/workflows/ci.yml

@@ -44,7 +44,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable, 1.65.0]
+        rust: [nightly, beta, stable, 1.70.0]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v3