Replace N/A with - everywhere (#24474)

Followup to https://github.com/go-gitea/gitea/pull/24427.

Reasoning is that `N/A` is specific to english while `-` is
language-neutral and does not need translation.

Before:
<img width="891" alt="Screenshot 2023-05-01 at 20 58 20"
src="https://user-images.githubusercontent.com/115237/235511592-8a36d0f2-34ff-4dbe-b642-67c0ade644fe.png">

After:
<img width="901" alt="Screenshot 2023-05-01 at 20 59 59"
src="https://user-images.githubusercontent.com/115237/235511594-d49f6d09-92e8-4e99-be7b-2a37f5d24129.png">

templates/repo/settings/webhook/history.tmpl

@@ -37,7 +37,7 @@
 										<span class="ui red label">{{.ResponseInfo.Status}}</span>
 									{{end}}
 								{{else}}
-									<span class="ui label">N/A</span>
+									<span class="ui label">-</span>
 								{{end}}
 							</a>
 							{{if or $.Permission.IsAdmin $.IsOrganizationOwner $.PageIsAdmin $.PageIsUserSettings}}
@@ -59,7 +59,7 @@
 								<h5>{{$.locale.Tr "repo.settings.webhook.payload"}}</h5>
 								<pre class="webhook-info"><code class="json">{{.PayloadContent}}</code></pre>
 							{{else}}
-								N/A
+								-
 							{{end}}
 						</div>
 						<div class="ui bottom attached tab segment" data-tab="response-{{.ID}}">
@@ -70,7 +70,7 @@
 								<h5>{{$.locale.Tr "repo.settings.webhook.body"}}</h5>
 								<pre class="webhook-info"><code>{{.ResponseInfo.Body}}</code></pre>
 							{{else}}
-								N/A
+								-
 							{{end}}
 						</div>
 					</div>