exclude toolchain/install/ in .gitignore after toolchain run (#6033)

* exclude toolchain/install/ to avoid accidental push after toolchain run

* also exclude toolchain/abacus_env.sh

Author: kluonj

.gitignore

@@ -22,3 +22,5 @@ time.json
 __pycache__
 abacus.json
 *.npy
+toolchain/install/
+toolchain/abacus_env.sh