action: generate version.txt

give github action the opportunity to generate this file .
If not existed ,  qmake will generate one

.github/workflows/windows-6.x-xapian.yml

@@ -75,8 +75,6 @@ jobs:
           previousTag=$(git tag --sort=-creatordate | sed -n 1p |cut -c 2-)
           echo "$previousTag">version.txt
           cat version.txt
-          pwd 
-          ls 
 
       # # msvc编译
       - uses: ilammy/msvc-dev-cmd@v1

goldendict.pro

@@ -13,7 +13,11 @@ system(git describe --tags --always --dirty): hasGit=1
     GIT_HASH=$$system(git rev-parse --short=8 HEAD )
 }
 
-system(echo $${VERSION}.$${GIT_HASH} on $${_DATE_} > version.txt)
+!exists( version.txt ) {
+      message( "generate version.txt...." )
+      system(echo $${VERSION}.$${GIT_HASH} on $${_DATE_} > version.txt)
+}
+
 
 !CONFIG( verbose_build_output ) {
   !win32|*-msvc* {