samples, tests: remove usage of space-separated lists

Convert them to native YAML lists. Support for space-separated
lists was deprecated in Twister a long time ago.

Signed-off-by: Gerard Marull-Paretas <gerard.marull@nordicsemi.no>

tests/arch/riscv/fatal/testcase.yaml

@@ -2,7 +2,9 @@ common:
   ignore_faults: true
   harness: console
   ignore_qemu_crash: true
-  tags: kernel riscv
+  tags:
+    - kernel
+    - riscv
   platform_allow:
     - qemu_riscv64
 tests:

tests/arch/riscv/userspace/riscv_gp/testcase.yaml

@@ -1,7 +1,9 @@
 common:
   ignore_faults: true
   ignore_qemu_crash: true
-  tags: kernel riscv
+  tags:
+    - kernel
+    - riscv
   platform_allow:
     - qemu_riscv64/qemu_virt_riscv64/smp
 tests: