Exclude acceptance-tagged overlay stress tests from CI

"Rust overlay SCP latency under TX load" and "Rust overlay 15-node 2000 TPS
stress test" are multi-node TPS benchmarks that were tagged [acceptance] but
still matched the CI TEST_SPEC via [overlay-ipc-large]. They time out on CI
runners when sharing CPU with the other test partitions (the 15-node test
uses ~136s of its 250s budget even on an idle 22-core machine). Filter
[acceptance] out of that group so CI runs the remaining [overlay-ipc-large]
coverage (10-node consensus) without the flaky benchmarks.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: SirTyson

ci-build.sh

@@ -212,7 +212,9 @@ echo "Using RND_SEED: $RND_SEED"
 ulimit -n 65536
 export INTERACTIVE=0
 
-export TEST_SPEC='[overlay-ipc],[loadgen],[overlay-ipc-large]'
+# Acceptance-tagged tests in [overlay-ipc-large] are multi-node TPS stress
+# benchmarks that need more CPU than CI runners provide; run them manually.
+export TEST_SPEC='[overlay-ipc],[loadgen],[overlay-ipc-large]~[acceptance]'
 export SKIP_SOROBAN_TESTS=true
 export STELLAR_OVERLAY_BINARY="${SRC_DIR}/build-${CC}-${PROTOCOL}/stellar-overlay"
 time make check