fix(plugins): use 'jsonc' instead of 'json' for code block language

The Block Kit CodeBlock type and Kumo's CodeBlock component use
'jsonc' for JSON content. Both webhook-notifier and sandboxed-test
were using 'json' which is not in the canonical set and would fail
validation if validateBlocks() were enforced.

While the blocks renderer now normalizes 'json' -> 'jsonc' as a
safety net, first-party plugins should use the canonical value.

Author: yomna-shousha

packages/plugins/sandboxed-test/src/sandbox-entry.ts

@@ -1259,7 +1259,7 @@ async function runSingleTestAdmin(ctx: PluginContext, testId: string) {
 					style: result.passed ? "success" : "error",
 					text: `${result.passed ? "PASS" : "FAIL"}: ${result.message}`,
 				},
-				...(result.details ? [{ type: "code", code: result.details, language: "json" }] : []),
+				...(result.details ? [{ type: "code", code: result.details, language: "jsonc" }] : []),
 			],
 			toast: {
 				message: `${testId}: ${result.passed ? "passed" : "failed"}`,

packages/plugins/webhook-notifier/src/sandbox-entry.ts

@@ -507,7 +507,7 @@ async function buildSettingsPage(ctx: PluginContext) {
 				},
 				{ type: "divider" },
 				{ type: "section", text: "**Payload Preview**" },
-				{ type: "code", code: payloadPreview, language: "json" },
+				{ type: "code", code: payloadPreview, language: "jsonc" },
 				{
 					type: "actions",
 					elements: [