chore(cli): update test output string for uutils cat

[holmanb]

When a file is not found the cat implementation in uutils
prints more output than the coreutils implementation.
Make pebble tests pass with uutils on Ubuntu 25.10.

Example output:

coreutils $ cat msg2
cat: msg2: No such file or directory

uutils $ cat msg2
cat: msg2: No such file or directory (os error 2)

[holmanb]

Seen on Ubuntu 25.10 from the tip of master:

----------------------------------------------------------------------
FAIL: cmd_enter_test.go:174: PebbleSuite.TestEnterExecReadServiceOutputFile

cmd_enter_test.go:192:
    c.Check(s.Stdout(), Equals, "foo\ncat: msg2: No such file or directory\n")
... obtained string = "" +
...     "foo\n" +
...     "cat: msg2: No such file or directory (os error 2)\n"
... expected string = "" +
...     "foo\n" +
...     "cat: msg2: No such file or directory\n"
... String difference:
...     [1]: "cat: msg2: No such file or directory (os error 2)" != "cat: msg2: No such file or directory"

Alternatively, we could switch the regex to replace the last characters of the current string \n with .*. Let me know.

[benhoyt]

Yeah, I would much rather we make the test more permissive (because we don't care so much about the exact message). So let's us .*.

[holmanb]

Yeah, I would much rather we make the test more permissive (because we don't care so much about the exact message). So let's us .*.

Thanks for the feedback. Agreed.

[benhoyt]

Thanks. Can you please add a PR description explaining the why/context of this change? And then I'll merge.

[holmanb]

Welcome. The relevant context is now included.