Merge bitcoin-core/gui#286: qt: Bump transifex slug for 22.x

417305991a qt: Bump transifex slug for 22.x (W. J. van der Laan)

Pull request description:

  Opening the 22.x translations early because of experimentation with the new xliff translations format. So change the slug so that the `tx` tool will fetch the right translation.

  In this context, change `file_filter` to use `xlf` as well as the files pulled with `tx pull` are that format now. The setting only affects the naming not the format of the files.

ACKs for top commit:
  hebasto:
    ACK 417305991a, I have reviewed the code and it looks OK, I agree it can be merged. All changes are in accordance with the Transifex [docs](https://docs.transifex.com/client/client-configuration).

Tree-SHA512: e0c18aa5e6cbd4428d24324fee8e5761b70dae51d0236277577aded719798c6a32fc81c0598f280321f2816629e33a334f61f9e7f6180c4074abfda6550cefbe

.tx/config

@@ -1,7 +1,7 @@
 [main]
 host = https://www.transifex.com
 
-[bitcoin.qt-translation-021x]
-file_filter = src/qt/locale/bitcoin_<lang>.ts
+[bitcoin.qt-translation-022x]
+file_filter = src/qt/locale/bitcoin_<lang>.xlf
 source_file = src/qt/locale/bitcoin_en.xlf
 source_lang = en