style: format isolation fixture test

(cherry picked from commit 2caf479)

Author: banteg

tests/test/plugin/test_isolation_fixtures.py

@@ -2,7 +2,7 @@
 
 import pytest
 
-isolation_source = '''import pytest
+isolation_source = """import pytest
 from brownie import Wei
 
 @pytest.fixture(autouse=True)
@@ -22,7 +22,7 @@ def test_isolation_first(accounts, web3, setup):
 
 def test_isolation_second(accounts, web3, setup):
     assert web3.eth.block_number == {1}
-    assert accounts[1].balance() == setup + Wei("{1} ether")'''
+    assert accounts[1].balance() == setup + Wei("{1} ether")"""
 
 
 @pytest.mark.parametrize("arg", ["", "-n 2"])