CI: fix-up txpush

- need to force-push the translation tag (since there's only one,
   and it moves through history whenever TX is pushed)
 - xmllint canonicalization removes the DOCTYPE, so hack in
   a pipeline stage that re-inserts it.

ci/txpush.sh

@@ -41,7 +41,7 @@ else
   # txtag is used to tag in git to measure changes
   txtag() {
     git tag -f translation
-    git push origin translation
+    git push --force origin translation
   }
 fi
 
@@ -83,7 +83,7 @@ $LUPDATE -no-obsolete $_srcdirs -ts lang/calamares_en.ts
 
 if test -n "$XMLLINT" ; then
   TS_FILE="lang/calamares_en.ts"
-  $XMLLINT --c14n11 "$TS_FILE" | $XMLLINT --format --encode utf-8 -o "$TS_FILE".new - && mv "$TS_FILE".new "$TS_FILE"
+  $XMLLINT --c14n11 "$TS_FILE" | { echo "<!DOCTYPE TS>" ; cat - ; } | $XMLLINT --format --encode utf-8 -o "$TS_FILE".new - && mv "$TS_FILE".new "$TS_FILE"
 fi
 
 tx push --source --no-interactive -r calamares.calamares-master