Change to GOPATH before go get

So it won't touch go.mod

Signed-off-by: Shengjing Zhu <zhsj@debian.org>

script/setup/install-cni-windows

@@ -21,6 +21,7 @@ WINCNI_BIN_DIR="${DESTDIR}/cni"
 WINCNI_PKG=github.com/Microsoft/windows-container-networking
 WINCNI_VERSION=aa10a0b31e9f72937063436454def1760b858ee2
 
+cd "$GOPATH"
 go get -d "${WINCNI_PKG}/..."
 cd "${GOPATH}/src/${WINCNI_PKG}"
 git checkout "${WINCNI_VERSION}"