Change property value from "1" to true in phpcs.xml.dist

The ignoreUnusedValuesWhenOnlyKeysAreUsedInForeach is a boolean value.
It should be set to true. If it is set to the string "1" Slevomat will
break with the following message:

PHP Fatal error:  Uncaught TypeError: Return value of
[...]\UnusedVariableSniff::isValueInForeachAndErrorIsIgnored() must be
of the type bool, string returned in
[...]/vendorr/slevomat/coding-standard/SlevomatCodingStandard/Sniffs/Variables/UnusedVariableSniff.php:528

This effects Slevomat 7.0.19.

Change-Id: I8a0277bb3ba977c76677f70aa57c079cd3becfab
Issue-Link: https://project.pronovix.net/issues/4735

config/phpcs.xml.dist

@@ -67,7 +67,7 @@
     <rule ref="SlevomatCodingStandard.PHP.UselessSemicolon"/>
     <rule ref="SlevomatCodingStandard.Variables.UnusedVariable">
         <properties>
-            <property name="ignoreUnusedValuesWhenOnlyKeysAreUsedInForeach" value="1"/>
+            <property name="ignoreUnusedValuesWhenOnlyKeysAreUsedInForeach" value="true"/>
         </properties>
     </rule>
     <rule ref="SlevomatCodingStandard.Variables.UselessVariable"/>