twister: Remove newline suffix in BinaryHandler

Update the code that removes newline suffix in BinaryHandler for
compatibility with python 3.8.

Fixes: https://github.com/zephyrproject-rtos/zephyr/issues/58335

Signed-off-by: Keith Short <keithshort@google.com>
diff --git a/scripts/pylib/twister/twisterlib/handlers.py b/scripts/pylib/twister/twisterlib/handlers.py
index 99045ef..91be15d 100755
--- a/scripts/pylib/twister/twisterlib/handlers.py
+++ b/scripts/pylib/twister/twisterlib/handlers.py
@@ -176,6 +176,8 @@
         self.line = proc.stdout.readline()
 
     def _output_handler(self, proc, harness):
+        suffix = '\\r\\n'
+
         with open(self.log, "wt") as log_out_fp:
             timeout_extended = False
             timeout_time = time.time() + self.timeout
@@ -188,7 +190,10 @@
                 reader_t.join(this_timeout)
                 if not reader_t.is_alive() and self.line != b"":
                     line_decoded = self.line.decode('utf-8', "replace")
-                    stripped_line = line_decoded.rstrip().removesuffix('\\r\\n')
+                    if line_decoded.endswith(suffix):
+                        stripped_line = line_decoded[:-len(suffix)].rstrip()
+                    else:
+                        stripped_line = line_decoded.rstrip()
                     logger.debug("OUTPUT: %s", stripped_line)
                     log_out_fp.write(line_decoded)
                     log_out_fp.flush()