Fixes git add . doesn't include scripts/buildtests.in

Reference issue

git add . doesn't include scripts/buildtests.in.

What does this implement/fix?

In .gitignore, there are rule to ignore *build* ref.

This rule makes scripts/buildtests.in be excluded when we run gid add ..

To fix this issue, this PR modify .gitignore to exclude scripts/buildtests.in.