docs(core): update symfony major version from 7 to 8

Author: vinceAmstoutz

.doctor-rst.yaml

@@ -75,16 +75,16 @@ rules:
     yaml_instead_of_yml_suffix: ~
 
     versionadded_directive_major_version:
-        major_version: 7
+        major_version: 8
 
     versionadded_directive_min_version:
-        min_version: '7.0'
+        min_version: '8.0'
 
     deprecated_directive_major_version:
-        major_version: 7
+        major_version: 8
 
     deprecated_directive_min_version:
-        min_version: '7.0'
+        min_version: '8.0'
 
 exclude_rule_for_file:
     - path: configuration/multiple_kernels.rst