bash's pattern substitution seems to leak some memory.

Issue

• The customer found that a bash script increases its memory consumption gradually which uses pattern substitution.
• Reproducer

  # cat test.sh
  a=00:00
  while :
  do
      b=${a/:/}
  done
  # sh test.sh

• Actual results

  # ps aux | grep [t]est.sh
  root     21877 78.0  0.1 113900  9084 pts/4    R+   09:49   0:01 sh test.sh
  # ps aux | grep [t]est.sh
  root     21877 93.3  0.1 120044 15268 pts/4    R+   09:49   0:02 sh test.sh
  # ps aux | grep [t]est.sh
  root     21877  105  0.2 126956 22236 pts/4    R+   09:49   0:04 sh test.sh
  # ps aux | grep [t]est.sh
  root     21877 93.3  0.3 133996 29196 pts/4    R+   09:49   0:05 sh test.sh
                           ^^^^^^^^^^^^