Minor changes to the build.zig files to prepare for Zig 0.11 (#1588)

Author: jedisct1

fiat-zig/build.zig

@@ -4,7 +4,7 @@ pub fn build(b: *std.Build) void {
     var main_tests = b.addTest(.{
         .root_source_file = .{ .path = "inversion.zig" },
     });
-
+    const run_main_tests = b.addRunArtifact(main_tests);
     const test_step = b.step("test", "Run tests");
-    test_step.dependOn(&main_tests.step);
+    test_step.dependOn(&run_main_tests.step);
 }