Investigate flaky parallel/test-fs-stat-bigint

[Trott]

• test file - parallel/test-fs-stat-bigint
• CI job arm/4326/RUN_SUBSET=1,label=pi2
• CI worker test-requireio_mcollina-debian9-armv7l_pi2-1
• output:

00:09:12 not ok 95 parallel/test-fs-stat-bigint
00:09:12   ---
00:09:12   duration_ms: 3.698
00:09:12   severity: fail
00:09:12   exitcode: 1
00:09:12   stack: |-
00:09:12     assert.js:86
00:09:12       throw new AssertionError(obj);
00:09:12       ^
00:09:12     
00:09:12     AssertionError [ERR_ASSERTION]: Expected values to be strictly equal:
00:09:12     + actual - expected
00:09:12     
00:09:12     + 1542874151832n
00:09:12     - 1542874151833n
00:09:12                   ^
00:09:12         at verifyStats (/home/iojs/build/workspace/node-test-binary-arm/test/parallel/test-fs-stat-bigint.js:65:14)
00:09:12         at Object.<anonymous> (/home/iojs/build/workspace/node-test-binary-arm/test/parallel/test-fs-stat-bigint.js:88:3)
00:09:12         at Module._compile (internal/modules/cjs/loader.js:722:30)
00:09:12         at Object.Module._extensions..js (internal/modules/cjs/loader.js:733:10)
00:09:12         at Module.load (internal/modules/cjs/loader.js:620:32)
00:09:12         at tryModuleLoad (internal/modules/cjs/loader.js:560:12)
00:09:12         at Function.Module._load (internal/modules/cjs/loader.js:552:3)
00:09:12         at Function.Module.runMain (internal/modules/cjs/loader.js:775:12)
00:09:12         at startup (internal/bootstrap/node.js:300:19)
00:09:12         at bootstrapNodeJSCore (internal/bootstrap/node.js:826:3)
00:09:12   ...

Haven't seen this one fail before. Off-by-one/rounding-truncation error?

I'll open a PR to add more info to the assertion and then we can close this unless/until it fails again.

[refack: edited info and added link to test file]

[refack]

Possible fix/clarify - #23821