Update the matrix.

Author: johnbillion

.github/workflows/coding-standards.yml

@@ -43,14 +43,16 @@ jobs:
     uses: johnbillion/plugin-infrastructure/.github/workflows/reusable-coding-standards.yml@stable-stubs
     strategy:
       matrix:
-        wp:
-          # Latest three stable:
-          - '6.5'
-          - '6.4'
-          - '6.3'
-        php:
-          - '8.2'
-          - '7.4'
+        include:
+          # Latest stable on PHP 8.3:
+          - wp: '6.5'
+            php: '8.3'
+          # Latest stable on PHP 7.4:
+          - wp: '6.5'
+            php: '7.4'
+          # Oldest supported on PHP 7.4:
+          - wp: '5.6'
+            php: '7.4'
       fail-fast: false
     with:
       wp: ${{ matrix.wp }}