Bug: get_assets() fails with 404 when release is fetched by tag in PyGithub 2.9.0

Summary

In PyGithub 2.9.0, when a release is fetched by tag name using repo.get_release("v1.2.3"), calling release.get_assets() results in a 404 error because the constructed URL is invalid.

Root Cause

PyGithub 2.9.0 introduced lazy loading for releases (PR #3403). When fetching a release by tag:

1. The code constructs a lazy object with URL: https://api.github.com/repos/owner/repo/releases/tags/TAG_NAME
2. The __postProcess method in Requester.py sets data["url"] to this GET URL (line 883)
3. The get_assets() method constructs the assets URL as f"{self.url}/assets"
4. This results in: https://api.github.com/repos/owner/repo/releases/tags/TAG_NAME/assets
5. This is not a valid GitHub API endpoint - it should be: https://api.github.com/repos/owner/repo/releases/RELEASE_ID/assets

Reproduction

from github import Github

gh = Github(auth=...)  # Use authenticated client
repo = gh.get_repo("owner/repo")

# Get release by tag
release = repo.get_release("v1.2.3")

# This fails with 404
assets = list(release.get_assets())

Expected Behavior

The release.url property should contain the canonical release URL with the numeric release ID, not the /tags/TAG_NAME URL used to fetch it.

Actual Behavior

github.GithubException.UnknownObjectException: 404 {"message": "Not Found", ...}

Workaround

Get the release by ID instead of by tag:

# Get the release ID first
releases = repo.get_releases()
for r in releases:
    if r.tag_name == "v1.2.3":
        release = repo.get_release(r.id)
        break

Suggested Fix

In Requester.py, the __postProcess() method should:

1. Check if the response contains an id field
2. If URL ends with /releases/tags/{tag}, reconstruct it as /releases/{id}
3. Set data["url"] to the canonical URL

Alternatively, ensure the GitHub API response always includes the proper url field, and only fallback to the request URL if it's missing.

Environment

• PyGithub version: 2.9.0
• Python version: 3.11+
• Works correctly in: PyGithub 2.8.1

Impact

This bug affects any code that:

• Fetches releases by tag name (common pattern)
• Attempts to download release assets
• Uses GitHub App authentication with private repositories (where assets require authentication)

Related Changes

• PR Use GET url or _links.self as object url #3421: "Use GET url or _links.self as object url" - introduced the __postProcess method
• PR More lazy objects #3403: "More lazy objects" - made releases lazy by default