fetch: refactor referrer policy util functions

[Uzlopak]

The helper function for the referrer policy are not that strict. This PR improves the spec conformance.

[Uzlopak]

@KhafraDev PTAL

[Uzlopak]

@KhafraDev
PTAL

[Uzlopak]

@KhafraDev PTAL

[Uzlopak]

@KhafraDev

Time to approve :D

[github-actions]

The backport to v6.x failed:

The process '/usr/bin/git' failed with exit code 1

To backport manually, run these commands in your terminal:

# Fetch latest updates from GitHub
git fetch
# Create a new working tree
git worktree add .worktrees/backport-v6.x v6.x
# Navigate to the new working tree
cd .worktrees/backport-v6.x
# Create a new branch
git switch --create backport-3706-to-v6.x
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 9c3ed661e77e21eab407771058b0601fa85bb697
# Push it to GitHub
git push --set-upstream origin backport-3706-to-v6.x
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-v6.x

Then, create a pull request where the base branch is v6.x and the compare/head branch is backport-3706-to-v6.x.