exiv2: use expat version range

[mayeut]

Specify library name and version: exiv2/all

expat<2.6.2 has known security issues. We can now use version range: c.f. #23277

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• I've read the contributing guidelines.
• I've used a recent Conan client version close to the currently deployed.
• I've tried at least one configuration locally with the conan-center hook activated.

[conan-center-bot]

Conan v1 pipeline ✔️

All green in build 3 (b0dbb074ef33279a1f7959562fea73828fa05f9f):

• exiv2/0.27.5:
  All packages built successfully! (All logs)

• exiv2/0.28.2:
  All packages built successfully! (All logs)

• exiv2/0.28.1:
  All packages built successfully! (All logs)

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Conan v2 pipeline ✔️

Note: Conan v2 builds are now mandatory. Please read our discussion about it.

All green in build 3 (b0dbb074ef33279a1f7959562fea73828fa05f9f):

• exiv2/0.27.5:
  All packages built successfully! (All logs)

• exiv2/0.28.2:
  All packages built successfully! (All logs)

• exiv2/0.28.1:
  All packages built successfully! (All logs)

[conan-center-bot]

This PR has been automatically merged due to Bump version or Bump dependencies label.
Read https://github.com/conan-io/conan-center-index/blob/master/docs/labels.md#bump-version to obtain more information.