Fix date component timezone in blogging prompts unit test

[dvdchr]

Refs wordpress-mobile/WordPress-iOS#18607 (review)

Description

Fixes an issue where unit tests for Blogging Prompts could fail locally depending on the system's timezone.

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⚠️ NOTE: Auto-merge is turned on. ⚠️

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Testing Details

If your timezone is behind UTC, simply run the unit tests and ensure that they pass. Especially this test case: BloggingPromptsServiceRemoteTests#test_fetchPrompts_returnsRemotePrompts.

Otherwise, you can set a temporary timezone modification in setUp and tearDown like so:

// BloggingPromptsServiceRemoteTests.swift

    override func setUp() {
        super.setUp()
        NSTimeZone.default = TimeZone(secondsFromGMT: -2 * 3600)! // Set timezone to UTC-2.
        // ...
    }

    override func tearDown() {
        super.tearDown()
        // ...
        NSTimeZone.default = NSTimeZone.system // Reset the timezone.
    }

• Please check here if your pull request includes additional test coverage.
• I have considered updating the version in the .podspec file.

[ScoutHarris]

✅ run the unit tests and ensure that they pass