windows build: fix build.sh "cp" cmd

was exiting with non-zero error code due to trying to copy directory

```
9cf9cdda331b565dd95b105d3fe987beefa113ac2c594d83783998017ad52d70  dist/electrum-4.1.4-16-g648fac709-portable.exe
020ceacb3a6fc5986d3ec271985c22c8646d2bb534536b8e2ab774924b21d58f  dist/electrum-4.1.4-16-g648fac709-setup.exe
e65dbbe24fe01e8635d4def088667e65d4e9763e2ab74cbc1aec616b3f2834bc  dist/electrum-4.1.4-16-g648fac709.exe
💬 INFO:  Done.
cp: -r not specified; omitting directory '/home/user/wspace/electrum/contrib/build-wine/../../contrib/build-wine/fresh_clone/electrum/contrib/build-wine/dist/electrum'
```

contrib/build-wine/build.sh

@@ -52,5 +52,5 @@ sudo docker run -it \
 # make sure resulting binary location is independent of fresh_clone
 if [ ! -z "$ELECBUILD_COMMIT" ] ; then
     mkdir --parents "$PROJECT_ROOT/contrib/build-wine/dist/"
-    sudo cp -f "$FRESH_CLONE/contrib/build-wine/dist"/* "$PROJECT_ROOT/contrib/build-wine/dist/"
+    sudo cp -f "$FRESH_CLONE/contrib/build-wine/dist"/*.exe "$PROJECT_ROOT/contrib/build-wine/dist/"
 fi