Avoid warning by Apptainer v1.2.3 about X509_USER_PROXY defined in both the...

Avoid warning by Apptainer v1.2.3 about X509_USER_PROXY defined in both the environment and the command line option

run-arc.sh

@@ -43,6 +43,7 @@ fi
 #
 apptainerImage="${thisDir}/nordugrid-arc6-client.sif"
 ${apptainer} exec \
+    --cleanenv \
     --env X509_USER_PROXY=/tmp/x509_user_proxy \
     --bind /etc/grid-security \
     --bind ${X509_USER_PROXY}:/tmp/x509_user_proxy \