Raise required compiler to rust 1.73

Required by the most recent release of bstr.

    error: package `bstr v1.11.0` cannot be built because it requires rustc 1.73 or newer, while the currently active rustc version is 1.71.1
    Either upgrade to rustc 1.73 or newer, or use
    cargo update -p [email protected] --precise ver
    where `ver` is the latest version of `bstr` supporting rustc 1.71.1

.github/workflows/ci.yml

@@ -24,7 +24,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [nightly, beta, stable, 1.71.0]
+        rust: [nightly, beta, stable, 1.73.0]
     timeout-minutes: 45
     steps:
       - uses: actions/checkout@v4