build: update to use the latest version of go-junit-report

`make test` failed for me on MacOS with this error:

```console
$ make test

...

=== installing go-junit-report
tar: Error opening archive: Unrecognized archive format
make[2]: ***
$
```

So it seems the version v2.0.0 of go-junit-report has a broken source
tarball

Going to the latest version v2.1.0 fixes the problem for me.

Signed-off-by: Michael Adam <obnox@samba.org>

build/makelib/golang.mk

@@ -201,7 +201,7 @@ $(GOFMT):
 $(GOJUNIT):
 	@echo === installing go-junit-report
 	@mkdir -p $(TOOLS_DIR)/tmp
-	@curl -sL https://github.com/jstemmer/go-junit-report/releases/download/v2.0.0/go-junit-report-v2.0.0-$(GOOS)-$(GOHOSTARCH).tar.gz | tar -xz -C $(TOOLS_DIR)/tmp
+	@curl -sL https://github.com/jstemmer/go-junit-report/releases/download/v2.1.0/go-junit-report-v2.1.0-$(GOOS)-$(GOHOSTARCH).tar.gz | tar -xz -C $(TOOLS_DIR)/tmp
 	@mv $(TOOLS_DIR)/tmp/go-junit-report $(TOOLS_DIR)
 	@rm -fr $(TOOLS_DIR)/tmp