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

contrib/devtools/copyright_header.py

@@ -320,15 +320,13 @@ def get_most_recent_git_change_year(filename):
 ################################################################################
 
 def read_file_lines(filename):
-    f = open(filename, 'r', encoding="utf8")
-    file_lines = f.readlines()
-    f.close()
+    with open(filename, 'r', encoding="utf8") as f:
+        file_lines = f.readlines()
     return file_lines
 
 def write_file_lines(filename, file_lines):
-    f = open(filename, 'w', encoding="utf8")
-    f.write(''.join(file_lines))
-    f.close()
+    with open(filename, 'w', encoding="utf8") as f:
+        f.write(''.join(file_lines))
 
 ################################################################################
 # update header years execution