text: Title: [Bug]: 'no module 'xformers'. Processing without' on fresh installation of v1.9.0
  Body: ### Checklist
  
  - [X] The issue exists after disabling all extensions
  - [X] The issue exists on a clean installation of webui
  - [ ] The issue is caused by an extension, but I believe it is caused by a bug in the webui
  - [X] The issue exists in the current version of the webui
  - [X] The issue has not been reported before recently
  - [ ] The issue has been reported before but has not been fixed yet
  
  ### What happened?
  
  Unable to use xformers attention optimization
  
  ### Steps to reproduce the problem
  
  1. clone git repo
  2. set directory python version to 3.10.6 using 'pyenv local'
  3. run 'bash webui.sh'
  
  ### What should have happened?
  
  The webui should have installed and used xformers as the attention optimization
  
  ### What browsers do you use to access the UI ?
  
  Brave
  
  ### Sysinfo
  
  [sysinfo.json](https://github.com/AUTOMATIC1111/stable-diffusion-webui/files/15014281/sysinfo.json)
  
  
  
  ### Console logs
  
  ```Shell
  Installing requirements
  Launching Web UI with arguments: 
  no module 'xformers'. Processing without...
  no module 'xformers'. Processing without...
  No module 'xformers'. Proceeding without it.
  Downloading: "https://huggingface.co/runwayml/stable-diffusion-v1-5/resolve/main/v1-5-pruned-emaonly.safetensors" to /media/origins/Games and AI/stable-diffusion-webui/models/Stable-diffusion/v1-5-pruned-emaonly.safetensors
  
  ...
  
  Applying attention optimization: Doggettx... done.
  ```
  
  
  ### Additional information
  
  Distro: Ubuntu 23.10
  Graphics Driver: 550.54.14
  CUDA Version: 12.4
  