Fix the "must check that an infinite loop is not triggered" scripting…

… integration test

This integration test fails intermittently because we're not correctly
awaiting typing actions, causing some characters to be missed in the
assertion. This commit fixes the issues by directly waiting for the
expected text area contents, similar to e.g. PR mozilla#18399 and PR mozilla#19001.

test/integration/scripting_spec.mjs

@@ -1282,24 +1282,17 @@ describe("Interaction", () => {
 
           await page.type(getSelector("28R"), "Hello");
           await page.waitForFunction(
-            `${getQuerySelector("28R")}.value !== "123"`
+            `${getQuerySelector("28R")}.value === "Hello123"`
           );
 
-          let text = await page.$eval(getSelector("28R"), el => el.value);
-          expect(text).withContext(`In ${browserName}`).toEqual("Hello123");
-
           // The action will trigger a calculateNow which itself
           // will trigger a resetForm (inducing a calculateNow) and a
-          // calculateNow.
+          // calculateNow. Without preventing against infinite loop
+          // the field is empty.
           await page.click("[data-annotation-id='31R']");
-
           await page.waitForFunction(
-            `${getQuerySelector("28R")}.value !== "Hello123"`
+            `${getQuerySelector("28R")}.value === "123"`
           );
-
-          // Without preventing against infinite loop the field is empty.
-          text = await page.$eval(getSelector("28R"), el => el.value);
-          expect(text).withContext(`In ${browserName}`).toEqual("123");
         })
       );
     });