mv: don't prompt to overwrite read-only file when stdin is not a terminal

[venoosoo]

This is the mv equivalent of #7492, which fixed the same issue for rm.

Changes:

• prompt_overwrite now skips the prompt when stdin is not a terminal and OverwriteMode is Default (implicit read-only protection), matching GNU mv behavior
• Added test test_mv_no_prompt_when_stdin_not_terminal

Fixes #11321

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/tail/tail-n0f is now being skipped but was previously passing.
Congrats! The gnu test tests/printf/printf-surprise is now passing!
Congrats! The gnu test tests/seq/seq-epipe is now passing!

[codspeed-hq]

Merging this PR will not alter performance

✅ 298 untouched benchmarks
⏩ 48 skipped benchmarks¹

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_{Comparing venoosoo:fix-mv-stdin-terminal (658f428) with main (bc58d3d)}

Footnotes

1. 48 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[oech3]

Please remove the hidden flag or restrict to debug build.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/date/date-locale-hour (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/pr/bounded-memory (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/printf/printf-surprise is now passing!