Exclude agent from windows tests (#9645)

We are aware of the issue, but while we are working on it,
having main tests broken is an annoyance.

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

tsdb/agent/db_test.go

@@ -11,6 +11,9 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+//go:build !windows
+// +build !windows
+
 package agent
 
 import (