Merge bitcoin/bitcoin#33391: test: Prevent disk space warning during node_init_tests

bdf01c6 test: Prevent disk space warning during node_init_tests (Ryan Ofsky)

Pull request description:

  mzumsande pointed out bitcoin/bitcoin#32345 (comment) that this test was print a warning:

  ```
  Warning: Disk space for "/tmp/test_common bitcoin/node_init_tests/init_test/bf78678cb7723a3e84b5/blocks" may not accommodate the block files. Approximately 810 GB of data will be stored in this directory.
  ```

  Fix by setting regtest instead of mainnet network before running the test.

ACKs for top commit:
  achow101:
    ACK bdf01c6
  Eunovo:
    Tested ACK bitcoin/bitcoin@bdf01c6:
  janb84:
    ACK bdf01c6
  l0rinc:
    tested ACK bdf01c6
  mzumsande:
    utACK bdf01c6
  enirox001:
    utACK bdf01c6

Tree-SHA512: ac4e1e48246c84a4c4b80ccb25e962b0090359ab0e541ee4f1a9e18ac9da8ec35a78c9a55501d231423053e945ff785862f0db141d4b620d622327670c764f8c

Author: achow101

src/test/node_init_tests.cpp

@@ -11,7 +11,12 @@
 
 using node::NodeContext;
 
-BOOST_FIXTURE_TEST_SUITE(node_init_tests, BasicTestingSetup)
+//! Like BasicTestingSetup, but using regtest network instead of mainnet.
+struct InitTestSetup : BasicTestingSetup {
+    InitTestSetup() : BasicTestingSetup{ChainType::REGTEST} {}
+};
+
+BOOST_FIXTURE_TEST_SUITE(node_init_tests, InitTestSetup)
 
 //! Custom implementation of interfaces::Init for testing.
 class TestInit : public interfaces::Init