[gdb/testsuite] Fix prompt regexp in batch-preserve-term-settings.exp

On openSUSE Leap 15.2, when running test-case
gdb.base/batch-preserve-term-settings.exp I get:
...
spawn /bin/sh^M
PS1="gdb-subshell$ "^M
sh-4.4$ PS1="gdb-subshell$ "^M
gdb-subshell$ PASS: gdb.base/batch-preserve-term-settings.exp: batch run: \
  spawn shell
...
but on Ubuntu 18.04.5, I get instead:
...
spawn /bin/sh^M
PS1="gdb-subshell$ "^M
$ gdb-subshell$ FAIL: gdb.base/batch-preserve-term-settings.exp: batch run: \
  spawn shell (timeout)
...

Fix this by making the regexp recognize the second pattern as well.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-12-16  Tom de Vries  <tdevries@suse.de>

	* gdb.base/batch-preserve-term-settings.exp:

---
 gdb/testsuite/gdb.base/batch-preserve-term-settings.exp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/gdb/testsuite/gdb.base/batch-preserve-term-settings.exp b/gdb/testsuite/gdb.base/batch-preserve-term-settings.exp
index c39d638aeb..3e35d20dd7 100644
--- a/gdb/testsuite/gdb.base/batch-preserve-term-settings.exp
+++ b/gdb/testsuite/gdb.base/batch-preserve-term-settings.exp
@@ -47,7 +47,7 @@ proc spawn_shell {} {
     set gotit 0
     set test "spawn shell"
     gdb_expect {
-	-re "PS1=\[^\r\n\]*\r\n$shell_prompt_re$" {
+	-re "PS1=\[^\r\n\]*\r\n.*$shell_prompt_re$" {
 	    pass $test
 	    set gotit 1
 	}