RFR: JDK-8016524: [macosx] Bottom line is not visible for JTableHeader [v3]

[Prasanta Sadhukhan]

On Mon, 31 Jan 2022 06:25:02 GMT, Harshitha Onkar <duke at openjdk.java.net> wrote:

>> The test is not marked for mac only and I see it fails in my ubuntu locally.
>> Did you try running the test in CI system?
>
> @prsadhuk I have changed the test case to explicitly set the table and header background to white. Mach5 tests are passing on all platforms including linux now. Can you please let me know in case you are seeing any issues on Ubuntu locally, with the new test case?

I now see it fail locally in windows system also along with ubuntu. windows screenshot here where the border is white which is why it fails
![JTheaderBorder](https://user-images.githubusercontent.com/43534309/151753660-92d6021a-30d6-4215-97b0-7ab17ddb88d4.png)

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PR: https://git.openjdk.java.net/jdk/pull/7219