sliceobject now has CPython copyright

Author: timfel

mx.graalpython/copyrights/overrides

@@ -124,6 +124,7 @@ graalpython/com.oracle.graal.python.cext/src/getcompiler.c,python.copyright
 graalpython/com.oracle.graal.python.cext/src/getversion.c,python.copyright
 graalpython/com.oracle.graal.python.cext/src/mysnprintf.c,python.copyright
 graalpython/com.oracle.graal.python.cext/src/pystrhex.c,python.copyright
+graalpython/com.oracle.graal.python.cext/src/sliceobject.c,python.copyright
 graalpython/com.oracle.graal.python.cext/src/unicodectype.c,python.copyright
 graalpython/com.oracle.graal.python.cext/src/unicodetype_db.h,python.copyright
 graalpython/com.oracle.graal.python.shell/src/com/oracle/graal/python/shell/GraalPythonMain.java,zippy.copyright