patch 8.2.5100: memory usage tests are not retried

Problem:    Memory usage tests are not retried.
Solution:   Mark memory usage tests as flaky.
diff --git a/src/testdir/test_memory_usage.vim b/src/testdir/test_memory_usage.vim
index 3b7b372..976fcde 100644
--- a/src/testdir/test_memory_usage.vim
+++ b/src/testdir/test_memory_usage.vim
@@ -65,6 +65,9 @@
   let self.job = term_getjob(self.buf)
   call WaitFor({-> job_status(self.job) ==# 'run'})
   let self.pid = job_info(self.job).process
+
+  " running an external command may fail once in a while
+  let g:test_is_flaky = 1
 endfunc
 
 func s:term_vim.stop() abort
diff --git a/src/version.c b/src/version.c
index e9cfe7c..74e8595 100644
--- a/src/version.c
+++ b/src/version.c
@@ -735,6 +735,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    5100,
+/**/
     5099,
 /**/
     5098,