extendr: Windows tests are failing

Several of the recent PRs have Windows tests failing with a stack overflow:

Error: Error: C stack usage  2101032 is too close to the limit
error: test failed, to rerun pass '--lib'
Error: i686-pc-windows-gnu

For example: https://github.com/extendr/extendr/pull/128/checks?check_run_id=1705514593#step:8:95

Since this seems to be happening with all recent PRs, I suspect it’s not related to them but some other cause.