[ci skip] Add note about --with-openssl-legacy-provider

Added here to have all build system configuration options changes also
at one place for easier overview.

Option added via GH-13951

Author: petk

UPGRADING.INTERNALS

@@ -118,6 +118,8 @@ PHP 8.4 INTERNALS UPGRADE NOTES
      ext/ftp and ext/mysqlnd is enabled implicitly, when building with
      ext/openssl (--with-openssl), or explicitly by using new configure options
      --with-ftp-ssl and --with-mysqlnd-ssl.
+   - New configure option --with-openssl-legacy-provider to enable OpenSSL
+     legacy provider.
    - COOKIE_IO_FUNCTIONS_T symbol has been removed (use cookie_io_functions_t).
    - HAVE_SOCKADDR_UN_SUN_LEN symbol renamed to HAVE_STRUCT_SOCKADDR_UN_SUN_LEN.
    - HAVE_UTSNAME_DOMAINNAME symbol renamed to HAVE_STRUCT_UTSNAME_DOMAINNAME.