[gdb/testsuite] Fix gdb.base/stap-probe.exp with read1

When running test-case gdb.base/stap-probe.exp with make target check-read1, I
run into this and similar:
...
FAIL: gdb.base/stap-probe.exp: without semaphore, not optimized: \
  info probes stap (timeout)
...

Fix this by using gdb_test_lines instead of gdb_test.

Tested on x86_64-linux.

gdb/testsuite/gdb.base/stap-probe.exp

@@ -134,10 +134,10 @@ proc stap_test {exec_name {args ""}} {
 	"check argument not at probe point"
 
     if {[string first "-DUSE_SEMAPHORES" $args] != -1} {
-	gdb_test "info probes stap" \
+	gdb_test_lines "info probes stap" "" \
 	    "test *user *$hex *$hex .*"
     } else {
-	gdb_test "info probes stap" \
+	gdb_test_lines "info probes stap" "" \
 	    "test *user *$hex .*"
     }