Use fileToPath()

[ghost]

This is a follow-up to PR #3210 on GitHub. See:
#3210 (comment)

Proposed changelog entries

None required

Submitter checklist

• JIRA issue is well described
• Changelog entry appropriate for the audience affected by the change (users or developer, depending on the change). Examples
  * Use the Internal: prefix if the change has no user-visible impact (API, test frameworks, etc.)
• Appropriate autotests or explanation to why this change has no tests
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Desired reviewers

@oleg-nenashev

[oleg-nenashev]

@dtrebbien thanks!

[oleg-nenashev]

@dtrebbien It seems that this change causes some flakiness in the PR builder. E.g. https://ci.jenkins.io/blue/organizations/jenkins/Core%2Fjenkins/detail/PR-3238/6/tests

[ghost]

Hello @oleg-nenashev

Examining the stacktrace and line 47 of TextFileTest.java, it appears that the issue is within TextFile.fastTail() (or maybe somehow the temporary copy of ascii.txt is not fully written before it is read or the temporary copy is overwritten in the meantime?). However, fastTail() is not modified by this PR.