with SAGE_CHECK=yes, one needs io installed to prevent hangs

Author: dimpase

build/pkgs/gap/spkg-check.in

@@ -3,6 +3,13 @@ cd src
 # #28728: Fix test failure in tst/testinstall/strings.tst
 export LC_CTYPE=en_US.UTF-8
 
+# #34391: in GAP 4.12 some packages need GAP package io
+#         to let tests run, otherwise this hangs. Thus we install io here.
+cd pkg/io
+./configure --with-gaproot=../..
+make
+cd ../..
+
 make testinstall
 if [[ $? -ne 0 ]]; then
     exit 1