Only provide the commit summary for Discord webhook push events (#32432) (#32447)

Backport #32432 by @kemzeb

Resolves #32371.

#31970 should have just showed the commit summary, but
`strings.SplitN()` was misused such that we did not perform any
splitting at all and just used the message. This was not caught in the
unit test made in that PR since the test commit summary was > 50 (which
truncated away the commit description).

This snapshot resolves this and adds another unit test to ensure that we
only show the commit summary.

Co-authored-by: Kemal Zebari <60799661+kemzeb@users.noreply.github.com>

services/webhook/discord.go

@@ -151,7 +151,7 @@ func (d discordConvertor) Push(p *api.PushPayload) (DiscordPayload, error) {
 	// for each commit, generate attachment text
 	for i, commit := range p.Commits {
 		// limit the commit message display to just the summary, otherwise it would be hard to read
-		message := strings.TrimRight(strings.SplitN(commit.Message, "\n", 1)[0], "\r")
+		message := strings.TrimRight(strings.SplitN(commit.Message, "\n", 2)[0], "\r")
 
 		// a limit of 50 is set because GitHub does the same
 		if utf8.RuneCountInString(message) > 50 {