v0.21.1 — Windows fix for the new test matrix

A test fix. No change to what the tool exports.

The scenario matrix added in 0.21.0 failed on Windows, and the fault was the matrix's own. It runs the browser extension's core in node and read the output with text=True, which decodes using the locale encoding, and that is cp1252 on Windows. One scenario deliberately carries Greek and Chinese to catch exactly this class of thing, and the first thing it caught was the test that runs it.

A rule now fails the build for any subprocess call that decodes with the locale encoding instead of naming one. It found two more immediately, in the theme detection. Neither is reachable on Windows, which reads the theme from the registry rather than a subprocess, so neither was a live bug, but both name their encoding now.

pip install --upgrade "overleaf-comments-export[gui,pdf]"