i18n(en): a few source fixes (#7089)
* use en-US quotes: _there are no quotes in the part of the text it refers to_
* small reword to fix `a issue`
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/7089
Reviewed-by: floss4good <floss4good@noreply.codeberg.org>
Reviewed-by: Gusted <gusted@noreply.codeberg.org>
Co-authored-by: 0ko <0ko@noreply.codeberg.org>
Co-committed-by: 0ko <0ko@noreply.codeberg.org>