Cross the Phar and WordPress dimensions

`use-phar: true` was excluded on trunk and `use-phar: false` on latest, which
made each fully determined by the other: the Phar was only ever tested against
WP latest, and source only against trunk. Two combinations therefore went
untested — including source against WP latest, which is the ordinary local
setup and arguably the most important one in the file.

Cross the two dimensions and drop only the combinations that add no signal.
Source against WP latest and the Phar against trunk both run now, the latter as
an early warning that a WP change has broken the released binary. Neither is
covered by the continue-on-error condition, so both can fail the build.

This takes the run from 155 jobs to 217. The 256-job matrix cap is the reason
the remaining source combinations are dropped rather than the whole cross
product being enabled, which would have needed 310.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Jy4dmjymj9VmoTBaqrV4iX

Author: claude

.github/workflows/testing.yml

@@ -82,11 +82,24 @@ jobs:
           - php: '7.4'
             object_cache: sqlite
 
-          # Phar usage match defaults 
-          - use-phar: true
-            wp: trunk
-          - use-phar: false
+          # Phar and source are separate dimensions, not aliases for a WP
+          # version. Previously `use-phar: true` was excluded on trunk and
+          # `use-phar: false` on latest, which made the two fully determined by
+          # each other: the Phar was only ever tested against WP latest and
+          # source only against trunk, so source-on-latest — the ordinary local
+          # setup — went untested entirely.
+          #
+          # Cross them instead, dropping only the combinations that add no
+          # signal, which keeps the run under the 256-job matrix cap. What this
+          # buys is source against WP latest, and the Phar against trunk as an
+          # early warning that a WP change has broken the released binary.
+          # Neither of those runs with continue-on-error, so both can fail the
+          # build.
+          - php: '7.4'
             wp: latest
+            use-phar: false
+          - dbtype: sqlite
+            use-phar: false
 
           # Limit ancient php on trunk
           - php: '7.4'