patch 8.2.0382: some tests fail when run under valgrind

Problem:    Some tests fail when run under valgrind.
Solution:   Increase timeouts.
diff --git a/src/testdir/test_channel.vim b/src/testdir/test_channel.vim
index e1f8a5e..af767d2 100644
--- a/src/testdir/test_channel.vim
+++ b/src/testdir/test_channel.vim
@@ -1999,15 +1999,15 @@
   endif
   let g:job = job_start(cmd, {})
   call job_stop(g:job)
-  sleep 10m
+  sleep 50m
   call assert_equal(-1, job_info(g:job).exitval)
   let g:job = job_start(cmd, {})
   call job_stop(g:job, 'term')
-  sleep 10m
+  sleep 50m
   call assert_equal(-1, job_info(g:job).exitval)
   let g:job = job_start(cmd, {})
   call job_stop(g:job, 'kill')
-  sleep 10m
+  sleep 50m
   call assert_equal(-1, job_info(g:job).exitval)
 endfunc