[Bug]: tables with nanoplot do not render in docx

### What happened?

```
library(crane)

res <- trial |>
select(age, marker, grade, response) |>
tbl_uvregression(
y = response,
method = glm,
method.args = list(family = binomial),
exponentiate = TRUE,
hide_n = TRUE
) |>
modify_column_merge(
pattern = "{estimate} (95% CI {ci}; {p.value})",
rows = !is.na(estimate)
) |>
modify_header(estimate = "**Odds Ratio**") |>
add_forest(table_engine = "gt")

pager::save_docx(res, "result.docx")
```

this result in a un-openable docx file. Note that `pager::save_html(res, "result.html")` works fine.

### Relevant log output

_No response_

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