[expr.call] Move period to end end of sentence (#7871)

Author: Andreas-Krug

source/expressions.tex

@@ -3614,7 +3614,7 @@
 initialized\iref{dcl.init,class.copy.ctor} with
 its corresponding argument,
 and each precondition assertion of the function
-is evaluated.\iref{dcl.contract.func}
+is evaluated\iref{dcl.contract.func}.
 If the function is an explicit object member function and
 there is an implied object argument\iref{over.call.func},
 the list of provided arguments is preceded by the implied object argument