fix: prevent page jumps due to textarea auto resizing (#7569)

The change prevents unnecessary resizing of the text field.

## Testing

- Compose some text e.g. in an issue
- Enter a lot of lines, until the compose field is as big as possible
- Move the screen up, the top of the compose field should leave the screen, but the last e.g. 5 lines should still be visible on the screen
- Append some text
- Make sure the textfield just gets bigger, but doesn't jump to the bottom of the page

Fixes #7522

Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7569
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Beowulf <beowulf@beocode.eu>
Co-committed-by: Beowulf <beowulf@beocode.eu>

web_src/css/editor/combomarkdowneditor.css

@@ -84,7 +84,7 @@
 }
 
 text-expander {
-  display: block;
+  display: flex;
   position: relative;
 }