[build] makepchinput.py: Fix ceb925ae:

This was appending "roottest" to the filter string, instead of *also* filtering "roottest".
roottest dictionaries will always have full path names, so veto "/roottest/".
Fixes 19 incremental failures that ceb925ae claimed to fix:

    projectroot.roottest.root.meta.roottest_root_meta_drawing
    projectroot.roottest.root.tree.split.roottest_root_tree_split_make
    projectroot.roottest.root.treeformula.parse.roottest_root_treeformula_parse_make
    projectroot.roottest.root.treeformula.sync.roottest_root_treeformula_sync_make
    projectroot.roottest.root.tree.selector.roottest_root_tree_selector_make
    projectroot.roottest.root.io.fakeClass.roottest_root_io_fakeClass_make
    projectroot.roottest.root.tree.addresses.roottest_root_tree_addresses_make
    projectroot.roottest.root.treeformula.retobj.roottest_root_treeformula_retobj_make
    projectroot.roottest.root.treeproxy.roottest_root_treeproxy_make
    projectroot.roottest.root.treeformula.schemaEvolution.roottest_root_treeformula_schemaEvolution_make
    projectroot.roottest.root.tree.evolution.roottest_root_tree_evolution_make
    projectroot.roottest.root.treeformula.array.roottest_root_treeformula_array_make
    projectroot.roottest.root.meta.tclass.roottest_root_meta_tclass_execState
    projectroot.roottest.root.meta.roottest_root_meta_runautoload_auto
    projectroot.roottest.root.collection.roottest_root_collection_execMissing
    projectroot.test.test_stresstmva_interpreted
    projectroot.roottest.root.io.evolution.roottest_root_io_evolution_make
    projectroot.roottest.root.io.datamodelevolution.roottest_root_io_datamodelevolution_make
    projectroot.roottest.root.tree.friend.roottest_root_tree_friend_make.