Accommodate Different Node.js Versions (14, 16, 18) in Test Suite

[ananzh]

Description
As we're now allowing users to run our application on Node.js versions 14, 16, and 18 (#4071), we have found that we need to make certain modifications to our tests for compatibility reasons. For example,

// ToDo: Remove this logic when Node 14 support is removed
const isNode14 = process.version.startsWith('v14.');

While this temporary solution works for now, we would like to open this issue to remind us removing and cleanup these tests. Pls search ToDo: Remove this logic when Node 14 support is removed to find all the three tests:

• packages/osd-config-schema/src/errors/schema_error.test.ts
• src/core/server/http/router/validator/validator.test.ts
• src/plugins/visualizations/server/saved_objects/visualization_migrations.test.ts