Integrated: Remove spurious `^` char from tarball name

[Maurizio Cimadamore]

As the title says, this simple patch removes a spurious `^` char in the replacement text of a substitution applied during the tarball generation.
Because of that, on Linux, the generated tarball has a topdir named `^jextract-<version>`.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jextract/pull/54/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=54&range=00
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jextract/pull/54.diff
  Fetch: git fetch https://git.openjdk.org/jextract pull/54/head:pull/54

PR: https://git.openjdk.org/jextract/pull/54