Ensure extension is installable on detected PHP version

[asgrim]

https://github.com/scoutapp/scout-apm-php/pull/235/files#r769592589 :

Noticed a bug in the CI pipeline, the shivammathur/setup-php action is installing scoutapm even though it should NOT on PHP 8.1, since we don't support it yet. Reported shivammathur/setup-php#542

I think the reasonable approach suggested in the above issue to take here is to check we are installing on a supported PHP version:

or you can add a check for PHP version in your config.m4 similar to how Xdebug does it and hard-fail to compile when not supported.

https://github.com/xdebug/xdebug/blob/e8088b2d301a825d23ad325f3a61b78db9375e25/config.m4#L16-L27

  AC_MSG_CHECKING([Check for supported PHP versions])
  PHP_XDEBUG_FOUND_VERSION=`${PHP_CONFIG} --version`
  PHP_XDEBUG_FOUND_VERNUM=`echo "${PHP_XDEBUG_FOUND_VERSION}" | $AWK 'BEGIN { FS = "."; } { printf "%d", ([$]1 * 100 + [$]2) * 100 + [$]3;}'`
  if test "$PHP_XDEBUG_FOUND_VERNUM" -lt "70300"; then
    AC_MSG_ERROR([not supported. Need a PHP version >= 7.3.0 and < 8.3.0 (found $PHP_XDEBUG_FOUND_VERSION)])
  else
    if test "$PHP_XDEBUG_FOUND_VERNUM" -ge "80300"; then
      AC_MSG_ERROR([not supported. Need a PHP version >= 7.3.0 and < 8.3.0 (found $PHP_XDEBUG_FOUND_VERSION)])
    else
      AC_MSG_RESULT([supported ($PHP_XDEBUG_FOUND_VERSION)])
    fi
  fi