test: tolerate duplicate watch change events

[trivikr]

This deflakes test-watch-file-shared-dependency by allowing the watcher
listener to ignore extra or partial changed events.

fs.watch() can emit more than one event for a single write. The test only
needs to verify that the dependency change eventually reports both owners, but
wrapping the whole listener in common.mustCall() made any additional watcher
event fail the test.

Refs: https://github.com/nodejs/node/actions/runs/27462359210/job/81178399610

Error Log

=== release test-watch-file-shared-dependency ===
Path: parallel/test-watch-file-shared-dependency
Error: --- stdout ---
Mismatched <anonymous> function calls. Expected exactly 1, actual 2.
    at Module.mustCall (/Users/runner/work/node/node/node/test/common/index.js:468:10)
    at TestContext.<anonymous> (file:///Users/runner/work/node/node/node/test/parallel/test-watch-file-shared-dependency.mjs:37:34)
    at Test.runInAsyncScope (node:async_hooks:226:14)
    at Test.run (node:internal/test_runner/test:1369:21)
    at Test.start (node:internal/test_runner/test:1242:17)
    at node:internal/test_runner/test:1867:71
    at node:internal/per_context/primordials:466:82
    at new Promise (<anonymous>)
    at new SafePromise (node:internal/per_context/primordials:435:3)
Command: out/Release/node --expose-internals --test-reporter=./test/common/test-error-reporter.js --test-reporter-destination=stdout /Users/runner/work/node/node/node/test/parallel/test-watch-file-shared-dependency.mjs

---

Assisted-by: openai:gpt-5.5

[mcollina]

lgtm