test: swap actual and expected in assertions

'test/parallel/test-fs-write.js' contains assertions where the first
argument provided is the expected value and the second value is the
actual value. This is backward from the documentation for assertions
like 'assert.strictEqual()' where the first value should be the actual
value being tested and the second value is the expected value.

PR-URL: https://github.com/nodejs/node/pull/23474


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Gireesh Punathil <gpunathi@in.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>