Changed unspecified locale log message from INFO to WARN

[arpavan]

Description

This is a very small log message change. For the log message that informs the user when the locale field is missing in the test plan file, the log type has been changed from INFO to WARN to better indicate the nature of the message. I have added one more unit test to specifically look for this, as this is a "required" user facing change.

This now looks like this -

Also a small branding related correction has been made to the testSettings.md readme - changed phrase PowerFx to Power Fx to comply with the correct terminology.

Checklist

• [X] The code change is covered by unit tests. I have added tests that prove my fix is effective or that my feature works
• [X] I have performed end-to-end test locally.
• [X] New and existing unit tests pass locally with my changes
• [X] I have commented my code, particularly in hard-to-understand areas
• [X] I have made corresponding changes to the documentation
• [X] My changes generate no new warnings
• [X] I used clear names for everything
• [X] I have performed a self-review of my own code

[github-actions[bot]]

Package	Line Rate	Branch Rate	Complexity	Health
Microsoft.PowerApps.TestEngine	93%	89%	800	✔
Summary	93% (2171 / 2330)	89% (490 / 548)	800	✔

Minimum allowed line rate is 50%