[3.12] gh-108927: Include new dir test/regrtestdata in the installati…

…on (GH-112765) (GH-112785)

(cherry picked from commit f8c0198)

Co-authored-by: Victor Stinner <vstinner@python.org>

Makefile.pre.in

@@ -2129,6 +2129,9 @@ TESTSUBDIRS=	idlelib/idle_test \
 		test/imghdrdata \
 		test/leakers \
 		test/libregrtest \
+		test/regrtestdata \
+		test/regrtestdata/import_from_tests \
+		test/regrtestdata/import_from_tests/test_regrtest_b \
 		test/sndhdrdata \
 		test/subprocessdata \
 		test/support \