prompt: update powerlevel10k submodule to the latest commit (#1784)

- New features:
  - Show On Command -- Display prompt segments conditional on the
    command being typed. Demo:
    https://raw.githubusercontent.com/romkatv/powerlevel10k-media/master/show-on-command.gif
  - `p10k display` -- Quickly hide or show different parts of prompt.
  - `p10k-on-*` hooks -- Get notified about prompt-related events.
- New prompt segments:
  - google_app_cred -- Google Application Credentials.
  - luaenv -- Lua version from https://github.com/cehoffman/luaen.
  - jenv -- Java version from https://github.com/jenv/jenv.
  - plenv -- Perl version from https://github.com/tokuhirom/plenv.
  - nnn -- Shell indicator for https://github.com/jarun/nnn.
- Important fixes:
  - Ctrl-C no longer shortens prompt when used to terminate a zle widget
    with transient prompt enabled.
  - Don't print warnings in instant prompt when OMZ is updating.
  - rust_version now properly recognized rustup overrides.
- Smoother rendering when using transient prompt.
- New style in `p10k configure`: Lean restricted to 8 colors.

modules/prompt/external/powerlevel10k

@@ -1 +1 @@
-Subproject commit 345d0644a9c1a242ff131bde915bbe234c3dd745
+Subproject commit c21961b53c137253020aeffca2b132fdd6bcb116