Merge bitcoin/bitcoin#24527: test: set segwit height back to 0 on regtest

5ce3057c8e test: set segwit height back to 0 on regtest (Martin Zumsande)

Pull request description:

  The change of `consensus.SegwitHeight` from 0 to 1 for regtest in #22818 had the effect that if I create a regtest enviroment with  current master (or 23.x), and then try to load this chain with an older version (22.x), I get an InitError
  `Witness data for blocks after height 0 requires validation. Please restart with -reindex`
  and have to reindex because `BLOCK_OPT_WITNESS` is no longer set for the Genesis block and `NeedsRedownload()` in validation returns `true` with an older version.
  That might be a bit annoying for tests that use a shared regtest dir with different versions.

  If people think this is enough of an issue to be worth fixing, I think it should also make it into 23.x

ACKs for top commit:
  theStack:
    Concept and code-review ACK 5ce3057c8e

Tree-SHA512: b0e89ff7fc953bc0ae929d2da44cde7149321d987fb4763934f6c9635d00d807129a50b459cc5e69e86bb1819e4b063b969486e8016a1cb8db8f905fa315653d

src/chainparams.cpp

@@ -397,7 +397,7 @@ public:
         consensus.BIP65Height = 1;  // Always active unless overridden
         consensus.BIP66Height = 1;  // Always active unless overridden
         consensus.CSVHeight = 1;    // Always active unless overridden
-        consensus.SegwitHeight = 1; // Always active unless overridden
+        consensus.SegwitHeight = 0; // Always active unless overridden
         consensus.MinBIP9WarningHeight = 0;
         consensus.powLimit = uint256S("7fffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff");
         consensus.nPowTargetTimespan = 14 * 24 * 60 * 60; // two weeks