test: Fix windows_spawn tmp directory cleanup

On Windows, a directory that's set as the current working directory is
not allowed to be removed. This can cause error on `deleteTree` if the
CWD is set to the file to be removed and will cause `error.FileBusy`.
However, due to `tmp.cleanup()` ignoring the errors, the folder removal error will
be ignored. The only test violating this is `windows_spawn`. As a
solution, setting the parent directory to be the CWD before deletion
will allow the cleanup to pass.

lib/std/fs/test.zig

@@ -1434,3 +1434,18 @@ test "delete a read-only file on windows" {
     file.close();
     try tmp.dir.deleteFile("test_file");
 }
+
+test "delete a setAsCwd directory on Windows" {
+    if (builtin.os.tag != .windows) return error.SkipZigTest;
+
+    var tmp = tmpDir(.{});
+    // Set tmp dir as current working directory.
+    try tmp.dir.setAsCwd();
+    tmp.dir.close();
+    try testing.expectError(error.FileBusy, tmp.parent_dir.deleteTree(&tmp.sub_path));
+    // Now set the parent dir as the current working dir for clean up.
+    try tmp.parent_dir.setAsCwd();
+    try tmp.parent_dir.deleteTree(&tmp.sub_path);
+    // Close the parent "tmp" so we don't leak the HANDLE.
+    tmp.parent_dir.close();
+}

test/standalone/windows_spawn/main.zig

@@ -116,6 +116,7 @@ pub fn main() anyerror!void {
 
     // Now let's set the tmp dir as the cwd and set the path only include the "something" sub dir
     try tmp.dir.setAsCwd();
+    defer tmp.parent_dir.setAsCwd() catch {};
     const something_subdir_abs_path = try std.mem.concatWithSentinel(allocator, u16, &.{ tmp_absolute_path_w, utf16Literal("\\something") }, 0);
     defer allocator.free(something_subdir_abs_path);