fix(sdk-coin-flrp): use regex in rejectedWith to match error substring

chai-as-promised rejectedWith(string) does exact match; use a regex
for partial matching of the HTTP 400 error message in the
createPairedWallet test.

Ticket: SI-287

Author: ashutoshkumar-6

modules/sdk-coin-flrp/test/unit/flrp.ts

@@ -1026,7 +1026,7 @@ describe('Flrp test cases', function () {
         .post(`/api/v2/tflrp/wallet/${walletId}/create-paired-wallet`)
         .reply(400, { error: 'Source FLR P wallet is not MPC (multisigType: onchain)' });
 
-      await basecoin.createPairedWallet({ walletId }).should.be.rejectedWith('Source FLR P wallet is not MPC');
+      await basecoin.createPairedWallet({ walletId }).should.be.rejectedWith(/Source FLR P wallet is not MPC/);
     });
   });
 });