diff-generate-patch.adoc: drop spurious backticks

Commit 0b080a70ab (doc: git-diff: apply format changes to diff-generate-patch, 2024-11-18) wrapped the ".." in mode <mode>,<mode>..<mode> in backticks. Note how the line before is quite similar, index <hash>,<hash>..<hash> but did not get any backticks. Remove the backticks, since they confuse Asciidoctor. The exact failure mode changed with c87b2b3a6f (doc: fix asciidoctor synopsis processing of triple-dots, 2025-04-12), and arguably to the better. But Asciidoctor (2.0.18) still ends up confused by these backticks and leaves the manpage rendering as index <hash>,<hash>..<hash> mode <mode>,<mode>`..__<mode>__ {empty}`new file mode <mode> Drop the backticks. This is a no-op with asciidoc (10.2.0). Signed-off-by: Martin Ågren <martin.agren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>