Try to support prompt_toolkit >3.0.37

Currently one test will fail with latest prompt_toolkit(3.0.43).
test_blank_line_fix will throw RuntimeError: no running event loop.
By bisecting commit, the culprit is
prompt-toolkit/python-prompt-toolkit@a775996.
This commit replaces custom `get_event_loop` with `asyncio.get_event_loop`.
The former will creator a new loop if `asyncio.get_running_loop` fails while the latter won't.
I mimic the changes in the examples to use `asyncio.run` and the test
passes.

Fixes: #344

pyproject.toml

@@ -33,7 +33,7 @@ license = "MIT"
 
 [tool.poetry.dependencies]
 python = ">=3.8"
-prompt_toolkit = ">=2.0,<=3.0.36"  # once https://github.com/prompt-toolkit/python-prompt-toolkit/issues/1726 is fixed, this can be changed to ">=2.0,<4.0"
+prompt_toolkit = ">=2.0,<4.0"
 
 [tool.poetry.group.docs]
 optional = true

tests/prompts/test_common.py

@@ -1,8 +1,10 @@
+import asyncio
 from unittest.mock import Mock
 from unittest.mock import call
 
 import pytest
 from prompt_toolkit.document import Document
+from prompt_toolkit.input.defaults import create_pipe_input
 from prompt_toolkit.output import DummyOutput
 from prompt_toolkit.styles import Attrs
 from prompt_toolkit.validation import ValidationError
@@ -13,7 +15,6 @@
 from questionary.prompts.common import InquirerControl
 from questionary.prompts.common import build_validator
 from questionary.prompts.common import print_formatted_text
-from tests.utils import execute_with_input_pipe
 from tests.utils import prompt_toolkit_version
 
 
@@ -72,7 +73,7 @@ def get_prompt_tokens():
 
     ic = InquirerControl(["a", "b", "c"])
 
-    def run(inp):
+    async def run(inp):
         inp.send_text("")
         layout = common.create_inquirer_layout(
             ic, get_prompt_tokens, input=inp, output=DummyOutput()
@@ -86,7 +87,8 @@ def run(inp):
             == 1000000000000000000000000000001
         )
 
-    execute_with_input_pipe(run)
+    with create_pipe_input() as inp:
+        asyncio.run(run(inp))
 
 
 def test_prompt_highlight_coexist():