Merge bitcoin/bitcoin#24993: test, contrib, refactor: use with when opening a file

027aab663a test, contrib, refactor: use `with` when opening a file (brunoerg)

Pull request description:

  When manipulating a file in Python without using `with()`, you have to close the file manually, so this PR does it in `get_block_hashes` (`contrib/linearize/linearize-data.py`).

  Edit: this PR does it for all occurances that previously weren't using `with`.

ACKs for top commit:
  laanwj:
    Code review ACK 027aab663a

Tree-SHA512: 879400968e0013e8678ec16f1fe5d0963a73c1e0d442ca34802d885214f0783d2e9a9b500fc6be7c3b93560a367b6a3d685eee24d2f9ce53fddf064ea6feecf8

test/functional/feature_config_args.py

@@ -247,7 +247,8 @@ class ConfArgsTest(BitcoinTestFramework):
         conf_file = os.path.join(default_data_dir, "bitcoin.conf")
 
         # datadir needs to be set before [chain] section
-        conf_file_contents = open(conf_file, encoding='utf8').read()
+        with open(conf_file, encoding='utf8') as f:
+            conf_file_contents = f.read()
         with open(conf_file, 'w', encoding='utf8') as f:
             f.write(f"datadir={new_data_dir}\n")
             f.write(conf_file_contents)

test/functional/feature_versionbits_warning.py

@@ -58,7 +58,8 @@ class VersionBitsWarningTest(BitcoinTestFramework):
 
     def versionbits_in_alert_file(self):
         """Test that the versionbits warning has been written to the alert file."""
-        alert_text = open(self.alert_filename, 'r', encoding='utf8').read()
+        with open(self.alert_filename, 'r', encoding='utf8') as f:
+            alert_text = f.read()
         return VB_PATTERN.search(alert_text) is not None
 
     def run_test(self):