[crac] RFR: 8370483: [CRaC] java/nio/file/spi/SetDefaultProvider.java test fails because of incorrect toFile() usage

[Voznia Anton]

Solved a regression. I used original approach as it is in the OpenJDK.

`java/nio/file/spi/SetDefaultProvider.java` test is passing.

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Commit messages:
 - 8370483: [CRaC] java/nio/file/spi/SetDefaultProvider.java test fails because of incorrect toFile() usage in crac

Changes: https://git.openjdk.org/crac/pull/270/files
  Webrev: https://webrevs.openjdk.org/?repo=crac&pr=270&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370483
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/crac/pull/270.diff
  Fetch: git fetch https://git.openjdk.org/crac.git pull/270/head:pull/270

PR: https://git.openjdk.org/crac/pull/270