qt: Bump transifex slug for 22.x

Opening the 22.x translations early because of experimentation with the
new xliff translations format.

In this context, change file_filter to `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).

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