text: Title: Edge case: subprocess call in @events.on_post_rc leads to suspending xonsh by OS
  Body: <!--- Provide a general summary of the issue in the Title above -->
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  ## xonfig
  
  <details>
  
  ```
  $ xonfig
  +------------------+----------------------------------+
  | xonsh            | 0.14.0                           |
  | Python           | 3.11.6                           |
  | PLY              | 3.11                             |
  | have readline    | True                             |
  | prompt toolkit   | 3.0.39                           |
  | shell type       | prompt_toolkit                   |
  | history backend  | json                             |
  | pygments         | 2.16.1                           |
  | on posix         | True                             |
  | on linux         | True                             |
  | distro           | unknown                          |
  | on wsl           | False                            |
  | on darwin        | False                            |
  | on windows       | False                            |
  | on cygwin        | False                            |
  | on msys2         | False                            |
  | is superuser     | False                            |
  | default encoding | utf-8                            |
  | xonsh encoding   | utf-8                            |
  | encoding errors  | surrogateescape                  |
  | xontrib          | []                               |
  | RC file 1        | /etc/xonsh/xonshrc               |
  | RC file 2        | /home/oskar/.config/xonsh/rc.xsh |
  +------------------+----------------------------------+
  ```
  
  </details>
  
  ## Expected Behavior
  
  Xonsh should launch normally and not become a background bash process.
  
  ## Current Behavior
  
  When a subprocess call is made in the `@events.on_post_rc` event, xonsh becomes a background process instead of the main process when launched from bash.
  
  ```
  ~ ✦ [18:56:59] ❯ xonsh
  [2]+  Stopped                 xonsh
  
  ✦ [18:56:37] ❯ 
  ```
  
  ## Steps to Reproduce
  This rc-file reproduces the issue for me
  
  ```
  @events.on_post_rc
  def __direnv_post_rc():
      r = $(ls)
  ```
  Then just start xonsh from bash.
  
  I stumbled upon this issue when loading the xonsh-direnv xontrib. So I have reported it there as well.
  
  
  ## For community
  ⬇️  **Please click the 👍 reaction instead of leaving a `+1` or 👍  comment**
  