MAINTAINERS: add tests to fpga area

Update MAINTAINERS file with file patterns related to area.

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/MAINTAINERS.yml b/MAINTAINERS.yml
index 27ce2ca..ce88bf7 100644
--- a/MAINTAINERS.yml
+++ b/MAINTAINERS.yml
@@ -820,6 +820,7 @@
     - dts/bindings/fpga/
     - include/zephyr/drivers/fpga.h
     - samples/drivers/fpga/
+    - tests/drivers/build_all/fpga/
   labels:
     - "area: FPGA"