build: fix pretty() sed invocation portability in .ver script

The `\0` being used to refer to the whole match is a GNU
extension. On other implementations of sed, this will simply
replace the each matched line with `	0;`, resulting in symbols
being missing in the NetworkManager executable, which breaks the
wifi plugin and others.

Use `&` instead, which behaves as expected in all implementations.

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/1562

tools/create-exports-NetworkManager.sh

@@ -71,7 +71,7 @@ get_symbols_missing() {
 }
 
 pretty() {
-    sed 's/.*/\t\0;/'
+    sed 's/.*/\t&;/'
 }
 
 do_build() {