patch 8.1.1929: no tests for text property popup window

Problem:    No tests for text property popup window.
Solution:   Add a few tests.
diff --git a/src/testdir/Make_all.mak b/src/testdir/Make_all.mak
index 80cf706..ee2a8f3 100644
--- a/src/testdir/Make_all.mak
+++ b/src/testdir/Make_all.mak
@@ -199,6 +199,7 @@
 	test_plus_arg_edit \
 	test_popup \
 	test_popupwin \
+	test_popupwin_textprop \
 	test_preview \
 	test_profile \
 	test_prompt_buffer \
@@ -388,6 +389,7 @@
 	test_perl.res \
 	test_plus_arg_edit.res \
 	test_popupwin.res \
+	test_popupwin_textprop.res \
 	test_preview.res \
 	test_profile.res \
 	test_prompt_buffer.res \