Merge bitcoin/bitcoin#26600: test: Set wallet type in test_runner when only one type is allowed

fadb8696dd test: Set wallet type in test_runner when only one type is allowed (MarcoFalke)

Pull request description:

  Currently devs are free to set or not set the wallet type in the test_runner when only one type is allowed to be set.

  This is inconsistent and causes review comments such as:

  * https://github.com/bitcoin/bitcoin/pull/24865#discussion_r1009752111

ACKs for top commit:
  achow101:
    ACK fadb8696dd

Tree-SHA512: 1ca0946df07b5bf6778fea957d74393757781c324d554fec2f7d03bf1915033e644d9a4c3d77e0b24090ab593d7ed3cb3c9169666bc39fff423706fceaa1af80

test/functional/test_framework/test_framework.py

@@ -448,11 +448,13 @@ class BitcoinTestFramework(metaclass=BitcoinTestMetaClass):
     # Public helper methods. These can be accessed by the subclass test scripts.
 
     def add_wallet_options(self, parser, *, descriptors=True, legacy=True):
-        group = parser.add_mutually_exclusive_group()
         kwargs = {}
         if descriptors + legacy == 1:
             # If only one type can be chosen, set it as default
             kwargs["default"] = descriptors
+        group = parser.add_mutually_exclusive_group(
+            # If only one type is allowed, require it to be set in test_runner.py
+            required=os.getenv("REQUIRE_WALLET_TYPE_SET") == "1" and "default" in kwargs)
         if descriptors:
             group.add_argument("--descriptors", action='store_const', const=True, **kwargs,
                                help="Run test using a descriptor wallet", dest='descriptors')