Build/Test Tools: Bump baseline version to 7.0.0 for the performance workflow

[mukesh27]

The performance benchmarking workflow currently uses WordPress 6.8.0 as its baseline for comparison, as updated in 60324.

With the successful launch of WordPress 7.0, the early 7.1 release cycle presents an excellent opportunity to update this baseline. Bumping the performance workflow baseline version to 7.0.0 will ensure that upcoming performance testing accurately measures regressions and improvements against the newest major milestone.

Current State & History

• Introduced: 55459 set the initial baseline to 6.1.1.
• First Bump: 59524 updated the baseline from 6.1.1 to 6.7.0.
• Second Bump: 60324 updated the baseline from 6.7.0 to 6.8.0.

Proposed Changes

Update the performance workflow configuration to use WordPress 7.0 as the new baseline version early in the 7.1 release cycle.

Trac ticket: https://core.trac.wordpress.org/ticket/65289

## Use of AI Tools

No

[desrosj]

I wouldn't have thought to use early here because it's not a feature that requires an extended testing period, but this does benefit all other work during the cycle to be in as soon as possible following a release.

I've also updated the ​Releasing Major Versions page in the Core Handbook to include the BASE_TAG as a variable that should be bumped after a new release is published so that this is always remembered in the future.

[desrosj]

In 62402:

Build/Test Tools: Bump baseline version for performance testing.

This ensures that the the performance testing workflow is providing meaningful data to track performance regressions and improvements.

Props mukesh27.
Fixes #65289.

This attempts to address memory exhaustion errors that have been happening any time the BASE_TAG within the performance testing workflow is set to any value higher than 6.7.0 by downloading the needed version of WordPress using WP-CLI inside the GitHub Actions runner instead of within the Docker environment.

• Most ​recent failure after bumping to 7.0.0.
• Previous attempts in r60324 was reverted in r60326.

Trac ticket: Core-65289.

## Use of AI Tools

None

[desrosj]

Reopening this because the same memory exhaustion issue has come up.

[desrosj]

In 62406:

Build/Test Tools: Change how BASE_TAG version is downlaoded.

Recent attempts to change the BASE_TAG version in the Performance Testing workflows in [60324] and [62402] have failed due to memory exhaustion errors when trying to download the version using WP-CLI in the local Docker environment.

While the. performance tests are run within the Docker environment, there’s no hard requirement for the wp core download command to happen through the wordpressdevelop/cli conatiner. This adjusts the workflow to perform the failing WP-CLI call within the GitHub Action runner and outside of Docker to avoid the memory exhaustion issue.

Props westonruter, swissspidy.
Fixes #65289.