Make sure task view can be rendered without a ti

[uranusjr]

Fix #18242, fix #18188.

These views should now work, but I want to add a couple of tests for these views as well.

[uranusjr]

Forgot to mention:

• The “task” view should now show “No Task Instance Available” instead of the “Task Instance Attributes” table (most of the values in the table are meaningless anyway since they are not “real” without an actual DAG run).
• The “rendered” view should work properly as in Airflow 2.1.x.

[eladkal]

LGTM
Tested locally. It solves the issue

[github-actions]

The PR is likely OK to be merged with just subset of tests for default Python and Database versions without running the full matrix of tests, because it does not modify the core of Airflow. If the committers decide that the full tests matrix is needed, they will add the label 'full tests needed'. Then you should rebase to the latest main or amend the last commit of the PR, and push it with --force-with-lease.