ci: build test_dgb_subsidy in both Linux test jobs (fix master-red NOT_BUILT)

test_dgb_subsidy is registered in test/CMakeLists.txt via
gtest_discover_tests but was never added to the explicit --target
allowlist in the build.yml Build tests / Build c2pool+tests steps, so
the executable is absent at ctest time and CTest registers the
test_dgb_subsidy_NOT_BUILT sentinel -> Run tests fails (exit 8) on both
the Linux x86_64 and Linux x86_64 (AsAN+UBSan) jobs. This has left
master CI red since #137 landed the test. Add the target to both
allowlists. Target builds clean and the 2 subsidy oracle tests pass.

Author: frstrtr

.github/workflows/build.yml

@@ -67,7 +67,7 @@ jobs:
                     test_phase4_embedded \
                     test_mweb_builder \
                     test_address_resolution test_compute_share_target \
-                    test_utxo \
+                    test_utxo test_dgb_subsidy \
                     v37_test \
             -j$(nproc)
 
@@ -193,7 +193,7 @@ jobs:
                     test_phase4_embedded \
                     test_mweb_builder \
                     test_address_resolution test_compute_share_target \
-                    test_utxo \
+                    test_utxo test_dgb_subsidy \
                     test_coin_broadcaster test_multiaddress_pplns test_pplns_stress \
                     v37_test \
             -j$(nproc)