RFR: 8302879: doc/building.md update link to jtreg builds

Mon Feb 20 21:57:25 UTC 2023

On Mon, 20 Feb 2023 16:34:32 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> The Eclipse Adoptium project recently moved its CI from ci.adoptopenjdk.net to ci.adoptium.net. The link to jtreg builds needs updating
>> 
>> See https://github.com/adoptium/infrastructure/issues/2932 for more context
>
> Looks fine to me.

@jerboaa are you happy to sponsor?

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PR: https://git.openjdk.org/jdk/pull/12665