Force copy over existing

(cherry picked from commit d866d4dc33)

tests/Makefile.am

@@ -108,10 +108,10 @@ hamlibdatetime.h: FORCE
 	if test -x $(top_srcdir)/.git ; then \
 		echo "/* This date time is from the last non-merge commit to Hamlib. */" > $@ ;\
 		echo "#define HAMLIBDATETIME "\"$$(TZ=UTC git --git-dir=$(top_srcdir)/.git log --no-merges --date='format-local:%a %b %d %H:%M:%S %Y %z SHA=' --format='%cd' -n 1)$$(git --git-dir=$(top_srcdir)/.git log --no-merges | grep commit | head -n 1 | cut -c8-13)\"  >> $@ ;\
-		cp $@ $(top_srcdir)/tests/$(@F) ;\
+		cp -f $@ $(top_srcdir)/tests/$(@F) ;\
 	fi
 	test -f $(top_srcdir)/tests/$(@F) || cp $(top_srcdir)/tests/$(@F).in $(top_srcdir)/tests/$(@F)
-	test -f $@ || cp $(top_srcdir)/tests/$(@F).in $@
+	test -f $@ || cp $(top_srcdir)/tests/$(@F) $@
 
 FORCE: