langref: fix build failure

doc/langref/bad_default_value.zig

@@ -17,7 +17,7 @@ pub fn main() !void {
         .maximum = 0.20,
     };
     const category = threshold.categorize(0.90);
-    try std.fs.File.stdout().writeAll(@tagName(category));
+    std.log.info("category: {t}", .{category});
 }
 
 const std = @import("std");

doc/langref/hello.zig

@@ -1,7 +1,17 @@
 const std = @import("std");
 
+// See https://github.com/ziglang/zig/issues/24510
+// for the plan to simplify this code.
 pub fn main() !void {
-    try std.fs.File.stdout().writeAll("Hello, World!\n");
+    var debug_allocator: std.heap.DebugAllocator(.{}) = .init;
+    defer _ = debug_allocator.deinit();
+    const gpa = debug_allocator.allocator();
+
+    var threaded: std.Io.Threaded = .init(gpa, .{});
+    defer threaded.deinit();
+    const io = threaded.io();
+
+    try std.Io.File.stdout().writeStreamingAll(io, "Hello, World!\n");
 }
 
 // exe=succeed