Issue #12497: Install test/data to prevent failures of the various codecmaps

tests.

Lib/test/data/README

 This empty directory serves as destination for temporary files
-created by some tests.
+created by some tests, in particular, the test_codecmaps_* tests.

Makefile.pre.in

@@ -912,7 +912,7 @@ MACHDEPS=	$(PLATDIR) $(EXTRAPLATDIR)
 XMLLIBSUBDIRS=  xml xml/dom xml/etree xml/parsers xml/sax
 LIBSUBDIRS=	tkinter tkinter/test tkinter/test/test_tkinter \
 		tkinter/test/test_ttk site-packages test \
-		test/capath \
+		test/capath test/data \
 		test/cjkencodings test/decimaltestdata test/xmltestdata \
 		test/subprocessdata \
 		test/tracedmodules test/encoded_modules \

Misc/NEWS

@@ -981,6 +981,9 @@ Extension Modules
 Tests
 -----
 
+- Issue #12497: Install test/data to prevent failures of the various codecmaps
+  tests.
+
 - Issue #12496: Install test/capath directory to prevent test_connect_capath
   testcase failure in test_ssl.