[fix] Updating an code host config maintains the correct unrestricted state

[pjlast]

Closes #58772

Fixes an issue where the logic that determines whether or not a code host connection is unrestricted differs between the code host connection creation and update code.

Test plan

Tests updated

[sourcegraph-bot]

Codenotify: Notifying subscribers in CODENOTIFY files for diff a8854c2...ecf38eb.

Notify	File(s)
@eseliger	internal/database/external_services.go internal/database/external_services_test.go

[eseliger]

good find! ty for test :)

[sourcegraph-release-bot]

The backport to 5.2 failed at https://github.com/sourcegraph/sourcegraph/actions/runs/7101937836:

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-5.2 5.2
# Navigate to the new working tree
cd .worktrees/backport-5.2
# Create a new branch
git switch --create backport-58772-to-5.2
# Cherry-pick the merged commit of this pull request and resolve the conflicts
git cherry-pick -x --mainline 1 12457a5bf22f7e4c5035b565597d11e274585e56
# Push it to GitHub
git push --set-upstream origin backport-58772-to-5.2
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-5.2

If you encouter conflict, first resolve the conflict and stage all files, then run the commands below:

git cherry-pick --continue
# Push it to GitHub
git push --set-upstream origin backport-58772-to-5.2
# Go back to the original working tree
cd ../..
# Delete the working tree
git worktree remove .worktrees/backport-5.2

• Follow above instructions to backport the commit.
• Create a pull request where the base branch is 5.2 and the compare/head branch is backport-58772-to-5.2., click here to create the pull request.
• Make sure to tag @sourcegraph/release-guild in the pull request description.
• Once the backport pull request is created, kindly remove the release-blocker from this pull request.