docs: fix formatting in supported PHP versions documentation

Signed-off-by: Felipe Sayão Lobato Abreu <github@mentordosnerds.com>

Author: coisa

docs/getting-started/supported-php-versions.rst

@@ -1,5 +1,5 @@
 Supported PHP Versions
-=====================
+======================
 
 The package targets modern PHP and ships configuration files that assume PHP
 8.3 language features and tooling support.
@@ -30,4 +30,4 @@ Practical Guidance
 - If a consumer library tests against newer engines, keep the local minimum at
   8.3 unless the library itself is intentionally raising its baseline.
 - When debugging dependency resolution, remember that the package sets
-  ``config.platform.php`` to ``8.3.0``.
+  ``config.platform.php`` to ``8.3.0``.