Remove uses of deprecated Join

cocotb has deprecated Join with the message "Using task directly is
prefered to Join(task) in all situations where the latter could be
used.". Awaiting on task is possible in all places where cocotb-bus
currently uses Join.

Unfortunately the newer approach is not supported on older versions of
cocotb. Accordingly two code paths have been introduced in the
problematic place. It is a test for cocotb-bus itself, therefore there's
no performance impact to check versions there.

tests/test_cases/test_axi4/test_axi4.py

@@ -7,6 +7,8 @@
 
 from random import randint, randrange, getrandbits
 
+from packaging.version import parse as parse_version
+
 import cocotb
 from cocotb.clock import Clock
 from cocotb.regression import TestFactory
@@ -424,9 +426,16 @@ async def test_simultaneous(dut, sync, num=5):
                      for address, value in zip(dummy_addrs, write_values)]
 
     read_values = []
-    for reader in readers:
-        read_values.append((await Join(reader))[0])
-    await Combine(*[Join(writer) for writer in dummy_writers])
+
+    if parse_version(cocotb.__version__) < parse_version("1.9.0"):
+        for reader in readers:
+            read_values.append((await Join(reader))[0])
+        await Combine(*[Join(writer) for writer in dummy_writers])
+    else:
+        for reader in readers:
+            await reader
+            read_values.append(reader.result()[0])
+        await Combine(*[cocotb.create_task(writer) for writer in dummy_writers])
 
     for i, (written, read) in enumerate(zip(write_values, read_values)):
         if written != read: