fix(webhook): keep line breaks in Telegram rich messages (#39650) (#39677)

Backport #39650 by @Kshot3000

Since the Telegram webhook switched to Bot API rich messages
(https://github.com/go-gitea/gitea/pull/38298), a bare newline in
`rich_message.html` is treated as insignificant whitespace, so
multi-line messages — issue and PR bodies, comments, push commit lists —
arrive in Telegram as a single paragraph. This restores the old layout
by converting line breaks (`\n`, `\r\n`, `\r`) to `<br>` in
`createTelegramPayloadHTML`, after sanitizing, covering every Telegram
payload type at once.

Verified: the new `Line breaks are kept in rich messages` test plus the
updated Push/Issue/IssueComment/PullRequest/Review expectations fail on
unpatched code (literal `\n` in the payload) and pass with the fix; the
full `services/webhook` package passes, gofmt/vet clean.

Fixes https://github.com/go-gitea/gitea/issues/39649

---
Tips welcome: PayPal kyleblake0659@gmail.com · BTC
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Co-authored-by: KShot <kshot9000@gmail.com>

services/webhook/telegram.go

@@ -201,9 +201,12 @@ func (telegramConvertor) WorkflowJob(p *api.WorkflowJobPayload) (TelegramPayload
 
 func createTelegramPayloadHTML(msgHTML string) TelegramPayload {
 	// https://core.telegram.org/bots/api#formatting-options
+	sanitized := strings.TrimSpace(string(markup.Sanitize(msgHTML)))
+	// Rich messages collapse bare newlines like HTML, so keep line breaks as <br>.
+	sanitized = strings.NewReplacer("\r\n", "<br>", "\r", "<br>", "\n", "<br>").Replace(sanitized)
 	return TelegramPayload{
 		RichMessage: InputRichMessage{
-			HTML: strings.TrimSpace(string(markup.Sanitize(msgHTML))),
+			HTML: sanitized,
 		},
 	}
 }