[JENKINS-72979] Remove trailing space from Windows agent secret file instructions

[debayangg]

See JENKINS-72979.

Testing done

Confirmed with interactive testing that when the space precedes the ">" character on Windows 11 cmd.exe, the output file includes a trailing space. Confirmed with interactive testing that when space that precedes the ">" character is removed, the output file does not include a trailing space.

No automated test because the text is an example command.

Proposed changelog entries

• Remove trailing space from Windows agent secret file instructions.

Proposed upgrade guidelines

N/A

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Desired reviewers

@NotMyFault

Before the changes are marked as ready-for-merge:

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[KalleOlaviNiemitalo]

I worried that, if ${it.jnlpMac} ends with a digit, then cmd.exe might treat that as part of a file descriptor redirection operator, like 2> to redirect standard error. But apparently cmd.exe doesn't do that if there are other printable characters adjacent to the last digit. And ${it.jnlpMac} is a hexadecimal number that doesn't contain spaces, so it's OK.