Dockerfile: update mvdan/shfmt to v3.8.0

- full diff: https://github.com/mvdan/sh/compare/v3.7.0...v3.8.0
- 3.7.0 release notes: https://github.com/mvdan/sh/releases/tag/v3.7.0
- 3.8.0 release notes: https://github.com/mvdan/sh/releases/tag/v3.8.0

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

Dockerfile

@@ -245,7 +245,7 @@ RUN --mount=type=cache,target=/root/.cache/go-build \
      && /build/gotestsum --version
 
 FROM base AS shfmt
-ARG SHFMT_VERSION=v3.6.0
+ARG SHFMT_VERSION=v3.8.0
 RUN --mount=type=cache,target=/root/.cache/go-build \
     --mount=type=cache,target=/go/pkg/mod \
         GOBIN=/build/ GO111MODULE=on go install "mvdan.cc/sh/v3/cmd/shfmt@${SHFMT_VERSION}" \