[PSM interop] Don't fail target if sub-target already failed (#33222)

We configured TestGrid to file bug separately for each failed
sub-target, if we still fail the main target, TestGrid will fail
duplicate bugs.

Author: XuanWang-Amos

tools/internal_ci/linux/grpc_xds_k8s_lb.sh

@@ -174,9 +174,6 @@ main() {
     run_test $test || (( ++failed_tests ))
   done
   echo "Failed test suites: ${failed_tests}"
-  if (( failed_tests > 0 )); then
-    exit 1
-  fi
 }
 
 main "$@"

tools/internal_ci/linux/grpc_xds_k8s_lb_python.sh

@@ -179,9 +179,6 @@ main() {
     run_test $test || (( ++failed_tests ))
   done
   echo "Failed test suites: ${failed_tests}"
-  if (( failed_tests > 0 )); then
-    exit 1
-  fi
 }
 
 main "$@"

tools/internal_ci/linux/grpc_xds_k8s_xlang.sh

@@ -131,9 +131,6 @@ main() {
   set +x
   echo "Failed test suites list: ${failed_string}"
   echo "Successful test suites list: ${successful_string}"
-  if (( failed_tests > 0 )); then
-    exit 1
-  fi
 }
 
 main "$@"

tools/internal_ci/linux/psm-security-python.sh

@@ -179,9 +179,6 @@ main() {
     run_test $test || (( ++failed_tests ))
   done
   echo "Failed test suites: ${failed_tests}"
-  if (( failed_tests > 0 )); then
-    exit 1
-  fi
 }
 
 main "$@"

tools/internal_ci/linux/psm-security.sh

@@ -163,9 +163,6 @@ main() {
     run_test $test || (( ++failed_tests ))
   done
   echo "Failed test suites: ${failed_tests}"
-  if (( failed_tests > 0 )); then
-    exit 1
-  fi
 }
 
 main "$@"