Build/Test Tools: Remove regular 6.2 & 6.3 branch performance testing.

Prior to WordPress 6.4, performance testing was performed using Puppeteer instead of Playwright (converted in [56926]). Because of the flaky nature of the workflow using Puppeteer, it was not converted to the reusable pattern implemented through #61213. It was instead removed from 6.2 and 6.3 in [58301] and [58330], respectively.

This removes the workflow for these branches from the strategy matrix when testing old branches to avoid errors and adds an expanded note about why those branches are missing.

See #61213, #61564.

git-svn-id: https://develop.svn.wordpress.org/trunk@58754 602fd350-edb4-49c9-b593-d223f7449a82

.github/workflows/test-old-branches.yml

@@ -92,17 +92,15 @@ jobs:
           - branch: '5.8'
             workflow: 'end-to-end-tests.yml'
 
-          # Performance testing was introduced in 6.2.
+          # Performance testing was introduced in 6.2 using Puppeteer but was overhauled to use Playwright instead in 6.4.
+          # Since the workflow frequently failed for 6.2 and 6.3 due to the flaky nature of the Puppeteer tests,
+          # the workflow was removed from those two branches.
           - branch: '6.6'
             workflow: 'performance.yml'
           - branch: '6.5'
             workflow: 'performance.yml'
           - branch: '6.4'
             workflow: 'performance.yml'
-          - branch: '6.3'
-            workflow: 'performance.yml'
-          - branch: '6.2'
-            workflow: 'performance.yml'
 
     # Run all branches monthly, but only the currently supported one twice per month.
     steps: