TYPO3 Core

in localconf.php I had (for whatever reason) 2 entries in the following order:
localconf.php
-----------------
$TYPO3_CONF_VARS['SYS']['compat_version'] = '4.0';
$TYPO3_CONF_VARS['SYS']['compat_version'] = '3.8';

Now running through the Installtool like:
InstallTool >>> 3: Update Wizard >>> 4.0 >>> accept all
confirmed that the needed changes would have been made;

however localconf.php still showed - in order:
-----------------
$TYPO3_CONF_VARS['SYS']['compat_version'] = '4.0';
$TYPO3_CONF_VARS['SYS']['compat_version'] = '3.8';

thus the instance was running 3.8;

PS: guess the second line was added manually at some point of time;
PPS: fix was manually deleting the 3.8 line;

(issue imported from #M4524)