Add AllowNoMatch attribute to hide no match warning

[jakobharder]

Background:
ModOps with no matches are inevitable when ensuring compatibility across several mods.
The current work around to avoid warnings is to add lots of fake data first - which is error prone and clutters mods needlessly.

Closes #176

Change:

1. Add check for [warning] and [error] to all test cases (via runner, test cases are untouched).
2. Add AllowNoMatch as an optional attribute to ModOps to switch the "no matching node found" message from warning to debug level.
3. Add unit tests to confirm the warning is produced without AllowNoMatch, and no warning is produced with the attribute.

[jakobharder]

Run doppelganger113/bazelisk-setup-action@v1.0.5
Error: Error: Request failed with status code 403

🤔

[jakobharder]

Why does the rerun work for you? I tried a few times on my forked repository and it always led to 403...

[jakobharder]

Implemented and refined on jakobharder:feature/loader10 for now.

I'm not sure if I want to keep AllowNoMatch though since Condition can do the same with a little more effort, but no loss of important warnings.