This commit ignores the sqlite3 database file under the `activerecord/test/storage/`.
- Steps to reproduce
```ruby
cd activerecord
bundle update sdoc --conservative # not relevant to this issue, just to update sdoc
bin/test test/cases/schema_dumper_test.rb -n test_do_not_dump_foreign_keys_when_bypassed_by_config
git status
```
- Without this fix, `git status` shows `test/storage/` as `Untracked files`.
Here `Gemfile.lock` difference is due to `bundle update sdoc --conservative`
```ruby
$ git status
On branch main
You are currently bisecting, started from branch 'main'.
(use "git bisect reset" to get back to the original branch)
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git restore <file>..." to discard changes in working directory)
modified: ../Gemfile.lock
Untracked files:
(use "git add <file>..." to include in what will be committed)
test/storage/
no changes added to commit (use "git add" and/or "git commit -a")
$
```
- With this fix, `git status` does not show any `Untracked files`.
```
$ git status
On branch add_gitignore_test_storage
You are currently bisecting, started from branch 'main'.
(use "git bisect reset" to get back to the original branch)
Changes not staged for commit:
(use "git add <file>..." to update what will be committed)
(use "git restore <file>..." to discard changes in working directory)
modified: ../Gemfile.lock
no changes added to commit (use "git add" and/or "git commit -a")
$
```
After running `bundle exec rake test:sqlite3` and `bundle exec rake test:sqlite3_mem`
on my VM I noticed that it had created untracked files:
```bash
vagrant@ubuntu-bionic:/rails/activerecord$ git status
Untracked files:
(use "git add <file>..." to include in what will be committed)
db/
file::memory:
```
To prevent them from being accidentally committed I put 'file::memory:' to
`activerecord/db/` folder and added the folder to .gitignore
Also, we could consider fixing this by removing `db/` folder in each test that
creates the folder.
It would be great if someone confirms that it happens not only on my VM.
* Global ignores at toplevel .gitignore
* Component-specific ignores in each toplevel directory
* Remove `actionview/test/tmp/.keep` for JRuby
```
rm actionview/test/tmp/ -fr
cd actionview/
bundle exec jruby -Itest test/template/digestor_test.rb
```
Related to #11743, #30392.
Closes#29978.
