wsdg backporting a patch: fix typo

When reading developer's guide about backporting,
it looks like the commit hash in this example is '1ab2c3d4',
and it is more consistent if we use 'backport-1ab2c3d4' instead of
'backport-g1ab2c3d4'.

This closes #19140

Signed-off-by: Jones Syue <jonessyue@qnap.com>

docbook/wsdg_src/wsdg_sources.adoc

@@ -925,7 +925,7 @@ You can do so as follows:
 [source,sh,subs="attributes+"]
 ----
 # Create a new topic branch for the backport.
-$ git checkout -b backport-g1ab2c3d4 upstream/{example-branch}
+$ git checkout -b backport-1ab2c3d4 upstream/{example-branch}
 
 # Cherry-pick the change. Include a "cherry picked from..." line.
 $ git cherry-pick -x 1ab2c3d4