fix(errorHandler): application errors would result in a 200 response

__tests__/server/ssrServer.spec.js

@@ -676,6 +676,7 @@ describe('ssrServer', () => {
         '"Fastify application error: method get, url "/example", correlationId "undefined", headersSent: false [Error: testing]"'
       );
       expect(renderStaticErrorPage).toHaveBeenCalledWith(request, reply);
+      expect(reply.code).toHaveBeenCalledWith(500);
     });
 
     test('setErrorHandler logs an error and renders the static error page with "headersSent" and "correlationId"', async () => {
@@ -709,6 +710,7 @@ describe('ssrServer', () => {
         '"Fastify application error: method get, url "/example", correlationId "123", headersSent: true [Error: testing]"'
       );
       expect(renderStaticErrorPage).toHaveBeenCalledWith(request, reply);
+      expect(reply.code).toHaveBeenCalledWith(500);
     });
   });
 });

src/server/ssrServer.js

@@ -227,6 +227,7 @@ async function appPlugin(fastify) {
 
     request.log.error('Fastify application error: method %s, url "%s", correlationId "%s", headersSent: %s', method, url, correlationId, headersSent, error);
 
+    reply.code(500);
     return renderStaticErrorPage(request, reply);
   });
 }