test: convert C6 secure boot tests to use ECDSA scheme

Author: mahavirj

examples/system/efuse/sdkconfig.ci.virt_secure_boot_v2.esp32c6

@@ -8,7 +8,8 @@ CONFIG_PARTITION_TABLE_CUSTOM_FILENAME="test/partitions_efuse_emul.csv"
 
 CONFIG_SECURE_BOOT=y
 CONFIG_SECURE_BOOT_V2_ENABLED=y
-CONFIG_SECURE_BOOT_SIGNING_KEY="test/secure_boot_signing_key.pem"
+CONFIG_SECURE_BOOT_V2_ECDSA_ENABLED=y
+CONFIG_SECURE_BOOT_SIGNING_KEY="test/secure_boot_signing_key_ecdsa_nistp256.pem"
 CONFIG_SECURE_INSECURE_ALLOW_DL_MODE=y
 
 # IMPORTANT: ONLY VIRTUAL eFuse MODE!