Free the desktop job's test binaries before its release build

The single CI runner has one 99 GB disk shared with its container images.
The desktop job reached 92 GB used (2.1 GB free) on v0.18.0's run, and on
v0.18.1's the release build died with "No space left on device", so that
tag has no release page. At rest the runner holds about 23 GB; the
restored target cache, the models and the dependency build bring a job to
about 78 GB before a test runs, and tests plus the release build take the
rest.

The test executables and examples in target/debug are the largest part
of that, are relinked whenever a source changes, and are not what the
cache exists for — the dependency rlibs are. Deleting them after the Test
step, before the release build, frees several GB at the moment the job
is fullest without costing the next run anything the cache would have
saved. The step prints the disk afterwards, beside the existing Disk
before/after lines.

.gitea/workflows/build-and-test.yml

@@ -157,6 +157,19 @@ jobs:
       - name: Test
         run: cargo test --workspace
 
+      # The runner has one 99 GB disk shared with its images, and this job
+      # ended at 92 GB (2.1 GB free) on v0.18.0's run; v0.18.1's release
+      # build then died with "No space left on device". The test executables
+      # and examples in target/debug are the largest things in it, are never
+      # reused (a changed source relinks them) and are not what the cache is
+      # for — the dependency rlibs are — so they go before the release build
+      # rather than competing with it.
+      - name: Free the test binaries before the release build
+        run: |
+          find target/debug/deps -maxdepth 1 -type f -executable -delete
+          rm -rf target/debug/examples target/debug/incremental
+          df -h /workspace 2>/dev/null || df -h .
+
       - name: Build
         run: cargo build --workspace --release