Reduce number of network reqs in visual regression

On my machine, this cuts down the test run time from ~5 mins to ~3 mins!

Closes #249

src/panel/visual-regression.test.ts

@@ -69,26 +69,17 @@ describe.each(parallelize(fixtures))("%s", (id, { rendererUrl }) => {
     });
   };
 
-  beforeEach(async () => {
-    await page.goto(rendererUrl, { waitUntil: "load" });
-    await page.mouse.move(0, 0);
-    await delay(500);
-  });
-
-  describe("landscape viewport", () => {
-    beforeEach(async () => {
+  describe("Go to page, test landscape and portrait viewport", () => {
+    it("matches landscape and portrait snapshot", async () => {
+      await page.goto(rendererUrl, { waitUntil: "load" });
+      await page.mouse.move(0, 0);
+      await delay(500);
       await page.setViewport({ width: 1200, height: 600 });
-    });
-
-    it("matches snapshot", () => matchSnapshot({ viewport: "landscape" }));
-  });
-
-  describe("portrait viewport", () => {
-    beforeEach(async () => {
+      await matchSnapshot({ viewport: "landscape" });
       await page.setViewport({ width: 600, height: 1200 });
+      await delay(500);
+      await matchSnapshot({ viewport: "portrait" });
     });
-
-    it("matches snapshot", () => matchSnapshot({ viewport: "portrait" }));
   });
 });