remove edge testing

Author: seuros

.github/workflows/ci.yml

@@ -42,7 +42,6 @@ jobs:
           - activerecord_7.0
           - activerecord_6.1
           - activerecord_6.0
-          - activerecord_edge
         adapter:
           - 'sqlite3:///:memory:'
           - mysql2://root:root@0/closure_tree_test

.gitignore

@@ -11,7 +11,6 @@ tmp/
 .yardoc/
 .rvmrc
 *.lock
-tmp/
 .ruby-*
 *.iml
 coverage/