minor fix for error message install to /proc/self/mem

[zhw2101024]

Fixes #12695.
Not added a test since no behavior changes in this PR.

[sylvestre]

i still would like to get a test :)
thanks

[zhw2101024]

i still would like to get a test :) thanks

The test has been commited.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/pr/bounded-memory (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/retry (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/tail/tail-n0f (fails in this run but passes in the 'main' branch)
Skipping an intermittent issue tests/cut/bounded-memory (passes in this run but fails in the 'main' branch)
Note: The gnu test tests/cp/link-heap is now being skipped but was previously passing.
Note: The gnu test tests/printf/printf-surprise is now being skipped but was previously passing.
Congrats! The gnu test tests/expand/bounded-memory is now passing!

[zhw2101024]

@oech3 all checks passed.