[CI] Disable jemalloc for running the JNI bindings tests

Summary:
This is incompatible:
https://github.com/jemalloc/jemalloc/issues/247

Test Plan: Run the build-secp256k1 CI build plan.

Reviewers: #bitcoin_abc, jasonbcox

Reviewed By: #bitcoin_abc, jasonbcox

Differential Revision: https://reviews.bitcoinabc.org/D6371