ZJIT: Add RUST_BACKTRACE=1 to zjit-macos.yml (ruby#16502)

Author: k0kubun

.github/workflows/zjit-macos.yml

@@ -55,6 +55,7 @@ jobs:
       RUN_OPTS: ${{ matrix.run_opts }}
       SPECOPTS: ${{ matrix.specopts }}
       TESTOPTS: ${{ matrix.testopts }}
+      RUST_BACKTRACE: 1
       ZJIT_RB_BUG: 1
 
     runs-on: macos-14