fix env var

Author: RCasatta

.github/workflows/rust.yml

@@ -43,7 +43,7 @@ jobs:
     - name: Run tests (Bitcoin mode with bitcoind 28.0, REST+Electrum)
       run: RUST_LOG=debug cargo test
       env:
-        BITCOIND_EXEC: ${{ github.workspace }}/bitcoin-28.0/bin/bitcoind
+        BITCOIND_EXE: ${{ github.workspace }}/bitcoin-28.0/bin/bitcoind
 
   test-electrum-raw:
     runs-on: ubuntu-22.04