Always protect at least one value on the timeline when running GC (#3357

)

### What
Now that GC has the abillity to protect data, turn the feature on for
our normal `purge_fraction_of_ram` operations.

Resolves: #1803

### Checklist
* [x] I have read and agree to [Contributor
Guide](https://github.com/rerun-io/rerun/blob/main/CONTRIBUTING.md) and
the [Code of
Conduct](https://github.com/rerun-io/rerun/blob/main/CODE_OF_CONDUCT.md)
* [x] I've included a screenshot or gif (if applicable)
* [x] I have tested [demo.rerun.io](https://demo.rerun.io/pr/3357) (if
applicable)

- [PR Build Summary](https://build.rerun.io/pr/3357)
- [Docs
preview](https://rerun.io/preview/678cf75238c49f71ab338a09cc99790de0626efa/docs)
<!--DOCS-PREVIEW-->
- [Examples
preview](https://rerun.io/preview/678cf75238c49f71ab338a09cc99790de0626efa/examples)
<!--EXAMPLES-PREVIEW-->
- [Recent benchmark results](https://ref.rerun.io/dev/bench/)
- [Wasm size tracking](https://ref.rerun.io/dev/sizes/)

crates/re_data_store/src/store_db.rs

@@ -377,8 +377,8 @@ impl StoreDb {
             target: re_arrow_store::GarbageCollectionTarget::DropAtLeastFraction(
                 fraction_to_purge as _,
             ),
-            gc_timeless: false,
-            protect_latest: 0,
+            gc_timeless: true,
+            protect_latest: 1,
             purge_empty_tables: false,
         });
         re_log::trace!(