loadSync: should not be able to load test file using protobufjs directly failed

[flaky-bot]

This test failed!

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---

commit: 393f6ca
buildURL: Build Status, Sponge
status: failed

Test output

ENOENT: no such file or directory, open '/workspace/test/fixtures/google/api/annotations.proto'
Error: ENOENT: no such file or directory, open '/workspace/test/fixtures/google/api/annotations.proto'
    at Object.openSync (fs.js:462:3)
    at Object.readFileSync (fs.js:364:35)
    at fetch (node_modules/protobufjs/src/root.js:172:34)
    at process (node_modules/protobufjs/src/root.js:133:29)
    at fetch (node_modules/protobufjs/src/root.js:178:13)
    at Root.load (node_modules/protobufjs/src/root.js:206:13)
    at Root.loadSync (node_modules/protobufjs/src/root.js:247:17)
    at Object.loadSync (node_modules/protobufjs/src/index-light.js:69:17)
    at Context. (build/test/load.test.js:53:31)
        -> /workspace/test/load.test.ts:67:27
    at processImmediate (internal/timers.js:461:21)

[bcoe]

Fixed by:

#448