Fix typo in tutorial documentation
Fix typo in tutorial documentation

This fixes a typo (`UA_VariableAttrbitues` -> `UA_VariableAttributes`) in the tutorial section 'Adding Variables to a Server'.
StalderT/open62541,StalderT/open62541,StalderT/open62541,open62541/open62541,JGrothoff/open62541,StalderT/open62541,open62541/open62541,open62541/open62541,jpfr/open62541,jpfr/open62541,open62541/open62541,jpfr/open62541,JGrothoff/open62541,JGrothoff/open62541,jpfr/open62541,JGrothoff/open62541