Allow clippy::unwrap-or-default because its usually wrong

`or_default` is generally less readable than writing out the thing
we're writing, as `Default` is opaque but explicit constructors
generally are not. Thus, we ignore the clippy lint (ideally we
could invert it and ban the use of `Default` in the crate entirely
but alas).

Author: TheBlueMatt

.github/workflows/build.yml

@@ -247,6 +247,8 @@ jobs:
       - name: Run default clippy linting
         run: |
           RUSTFLAGS='-D warnings' cargo clippy -- \
+                `# Things that are more readable in the non-clippy-enforce version` \
+                -A clippy::unwrap-or-default
                 `# Errors` \
                 -A clippy::erasing_op \
                 -A clippy::never_loop \