fix validate-headers target

Signed-off-by: Silvin Lubecki <silvin.lubecki@docker.com>

Dockerfile

@@ -58,7 +58,7 @@ RUN --mount=type=cache,target=/root/.cache/go-build \
 FROM builder AS validate-headers
 RUN --mount=type=cache,target=/root/.cache/go-build \
     --mount=type=cache,target=/go/pkg \
-    go get -u github.com/kunalkushwaha/ltag && ./scripts/validate/fileheader
+    go install github.com/kunalkushwaha/ltag@latest && ./scripts/validate/fileheader
 
 ####
 # CHECK GO MOD

scripts/validate/fileheader

@@ -19,7 +19,7 @@ set -eu -o pipefail
 
 if ! command -v ltag; then
     >&2 echo "ERROR: ltag not found. Install with:"
-    >&2 echo "    go get -u github.com/kunalkushwaha/ltag"
+    >&2 echo "    go install github.com/kunalkushwaha/ltag@latest"
     exit 1
 fi