move zig version responsibilities to build.zig.zon

.gitea/workflows/zig-build.yaml

@@ -13,8 +13,6 @@ jobs:
         uses: actions/checkout@v4
       - name: Setup Zig
         uses: https://github.com/mlugg/setup-zig@v2.0.5
-        with:
-          version: 0.15.1
       - name: Build project
         run: zig build --summary all
       - name: Run tests

build.zig.zon

@@ -2,6 +2,7 @@
     .name = .smithy,
     .version = "1.0.0",
     .fingerprint = 0xccfd3d0281810cb8,
+    .minimum_zig_version = "0.15.1",
     .paths = .{
         "build.zig",
         "build.zig.zon",