Bump `helm-unittest` helm plugin version to v0.5.1

[jenkins-infra-updatecli[bot]]

Bump `helm-unittest` helm plugin version

Update helm-unittest version in the GitHub Action workflow

change detected: * key "$.env.UNITTEST_VERSION" updated from "v0.5.0" to "v0.5.1", in file ".github/workflows/test.yml"

v0.5.1

Release published on the 2024-05-11 11:21:40 +0000 UTC at the url https://github.com/helm-unittest/helm-unittest/releases/tag/v0.5.1

**Fixes**
- Fix parse multidocument testsuites (credits @ivankatliarchuk, resolves #329, resolves #336)

**Updates**
- Update packages to latest patch versions
- Update documentation (credits @dancer1325)

Jenkins pipeline link

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