[DEVOPS-3035] jenkins test: fix for case of no YBC available

Summary:
Unfortunately, test script has option set option to exit for any command
failure, so running find on nonexistent dir fails out, even though that
is expected case on some platforms.

Test Plan: Jenkins: build platform: mac12

Reviewers: jharveysmith, skarri

Reviewed By: skarri

Subscribers: devops

Differential Revision: https://phorge.dev.yugabyte.com/D32955

build-support/jenkins/test.sh

@@ -208,7 +208,10 @@ THIRDPARTY_BIN=$YB_SRC_ROOT/thirdparty/installed/bin
 export PPROF_PATH=$THIRDPARTY_BIN/pprof
 
 # Check for available YBC
-ybc_tar=$(find /opt/yb-build/ybc/ -type f | sort -V | tail -1)
+ybc_tar=""
+if [[ -d /opt/yb-build/ybc ]]; then
+  ybc_tar=$(find /opt/yb-build/ybc/ -type f | sort -V | tail -1)
+fi
 ybc_dest="$YB_SRC_ROOT/build/ybc"
 if [[ -n ${ybc_tar} ]]; then
   log "Unpacking ${ybc_tar} binaries to ${ybc_dest}/"