add dependent modules regardless of whether a runner was specified

[elerch]

This addresses #23610 and very possibly #23453. The diff is semanticly equivalent to this diff, just cleaned up to remove the block that became unnecessary. All behavior tests pass.

diff --git i/src/main.zig w/src/main.zig
index 107599384..50363c68d 100644
--- i/src/main.zig
+++ w/src/main.zig
@@ -3040,7 +3040,6 @@ fn buildOutputType(
                 .builtin_mod = main_mod.getBuiltinDependency(),
                 .builtin_modules = null, // `builtin_mod` is specified
             });
-            test_mod.deps = try main_mod.deps.clone(arena);
             break :test_mod test_mod;
         } else try Package.Module.create(arena, .{
             .global_cache_directory = global_cache_directory,
@@ -3060,6 +3059,7 @@ fn buildOutputType(
             .builtin_modules = null, // `builtin_mod` is specified
         });

+        test_mod.deps = try main_mod.deps.clone(arena);
         break :root_mod test_mod;
     } else main_mod;