Bug: password in end of file with first line in pattern file won't work

### Environment
Win10 with git bash
### Case
target secret file: test.txt (should be the end of file without newline)
> password=12345

pattern file: pattern.txt (should be the first line of file)
> password\s*=\s*.+

Apply pattern:
`git secrets --add-provider -- cat ./pattern.txt`

Run scan:
`git secrets --scan`

An then it'll ignore the password.

Reproduce the report in Win10 Git Bash with test.txt ending without a newline, pattern.txt containing the first-line pattern, and the two commands shown. Start at the git secrets --add-provider and git secrets --scan entry points, then verify that the pattern matches the password at end of file and add a regression check for this case.

Written by the indexing model from the issue text.