Bug: diff.external --no-ext-diff suppresses --color-moved

Hello,

I configured "diff.extern" but use aliases for "diff --no-ext-diff". This combination suppresses --color-moved (as well as the corresponding config "diff.colorMoved").

What did you do before the bug happened? (Steps to reproduce your issue)
  1. Prepare ~/.gitconfig:
            [diff]
               #external = echo
  2. In some repository, create a moved-lines diff between index and working
     directory.
     For example, commit this file (the next 9 lines verbatim):
            line 1 first one
            line 2 second two
            line 3 third three
            line 4 fourth four
            line 5 fifth five
            line 6 sixth six
            line 7 seventh seven
            line 8 eighth eight
            line 9 ninth nine
     Then, edit it (moving lines exactly) to:
            line 4 fourth four
            line 5 fifth five
            line 6 sixth six
            line 7 seventh seven
            line 8 eighth eight
            line 9 ninth nine
            line 1 first one
            line 2 second two
            line 3 third three
     In this state, the command 'git diff --color-moved' should highlight
     changes as line moves with default colors purple/cyan.
  3. In ~/.gitconfig, uncomment 'external'.
  4. In the same repository, trigger the bug by running:
            git diff --no-ext-diff --color-moved

What did you expect to happen? (Expected behavior)

  The diff should be recognized as moving lines and colorized accordingly. By
  default in purple/cyan.
  The diff should NOT be colorized red/green.

What happened instead? (Actual behavior)

  The diff is colorized in red/green.

What's different between what you expected and what actually happened?

  The colorization is expected to indicate moved lines.
  The actual colorization indicates deletion/insertion, as if '--color-moved' is
  ignored.

Anything else you want to add:

  - I assume this bug is up to date with the 'next' branch, because the command
            git log v2.45.2..origin/next | grep "no-ext"
    finds no match in the repository from github.
  - Works the same in the older v2.25.1
  - Works the same with 'diff.colorMoved' instead of --color-moved
  - Works the same for other values of 'diff.external'
  - Works the same when setting custom colors for 'color.diff.oldMoved' etc.
  - Works not the same when using --no-ext-diff alone. Only when using
    diff.external as well.

[System Info]
git version:
git version 2.45.2
cpu: x86_64
no commit associated with this build
sizeof-long: 8
sizeof-size_t: 8
shell-path: /bin/sh
uname: Linux 5.15.0-107-generic #117~20.04.1-Ubuntu SMP Tue Apr 30 00:00:00 2024 x86_64
compiler info: gnuc: 9.4
libc info: glibc: 2.31
$SHELL (typically, interactive shell): /bin/bash

[Enabled Hooks] (none)