Change in tab indentation upon opening the file for writing

Question

I am reading a bunch of js files using Python. I am finding out the tags: section and updating it with additional values. My script is changing the previous indentation of the tags, especially for the closing bracket ].

Here is what my loop looks like:

def update_js_file(filename: str, tags: list) -> None:
    content = ''
    with open(filename, 'r', encoding='utf-8') as f:
        content = f.read()

    tags_raw = json.dumps(tags, indent=4)
    content = re.sub(r'tags: \[.+?\]', 'tags: ' + tags_raw, content, flags=re.DOTALL)
    with open(filename, 'w', encoding='utf-8') as f:
        f.write(content)

Git diff shows the following change in file:

     tags: [
-      "aws",
-      "cloudtrail",
-      "cap-04",
-      "mon-08"
-    ],
+    "aws",
+    "cloudtrail",
+    "cap-04",
+    "mon-08",
+    "NIST-800-171",
+    "NIST-800-171-3.3.8"
+],

How can I avoid this change in indentation for each tag and the closing bracket.

Edit: I was able to fix the indentation by changing the value of indentation to 8 in tags_raw but I am still not able to properly indent the closing bracket ].