test: improve assertion in test-require-dot

Include the value that differed from the expected value in an assertion
message in test-require-dot.

PR-URL: #16805
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>

test/parallel/test-require-dot.js

@@ -14,5 +14,8 @@ process.env.NODE_PATH = fixtures.path('module-require', 'relative');
 m._initPaths();
 
 const c = require('.');
-
-assert.strictEqual(c.value, 42, 'require(".") should honor NODE_PATH');
+assert.strictEqual(
+  c.value,
+  42,
+  `require(".") should honor NODE_PATH; expected 42, found ${c.value}`
+);