RFR: Fix formatting in sample/time

[Per Minborg]

This PR formats the time so that single-digit minutes will look better.

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Commit messages:
 - Fix formatting in sample/time

Changes: https://git.openjdk.org/jextract/pull/73/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=73&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/73.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/73/head:pull/73

PR: https://git.openjdk.org/jextract/pull/73