Only send the PID of the last process in a job to builtin fg

jobs -p %1 prints all processes in the first job.
fg is special because it only takes one argument.  Using the last process
in the pipeline works for the cases I can think of.

Fixes #7406

CHANGELOG.rst

@@ -138,6 +138,7 @@ Interactive improvements
 -  The fish Web configuration tool (``fish_config``) shows prompts correctly on Termux for Android (#7298) and detects Windows Services for Linux 2 properly (#7027).
 -  ``funcsave`` has a new ``--directory`` option to specify the location of the saved function (#7041). 
 -  ``help`` works properly on MSYS2 (#7113).
+-  Resuming a piped job by its number, like ``fg %1`` has been fixed (#7406).
 
 
 New or improved bindings

share/config.fish

@@ -226,11 +226,14 @@ function __fish_expand_pid_args
     end
 end
 
-for jobbltn in bg fg wait disown
+for jobbltn in bg wait disown
     function $jobbltn -V jobbltn
         builtin $jobbltn (__fish_expand_pid_args $argv)
     end
 end
+function fg
+    builtin fg (__fish_expand_pid_args $argv)[-1]
+end
 
 function kill
     command kill (__fish_expand_pid_args $argv)