Add RUST_BACKTRACE=1 to .github

Should help resolve the coordinator tests, which are failing in the current CI.
Presumably a timeout which is too low for the CI's slower runners.

.github/workflows/common-tests.yml

@@ -26,7 +26,7 @@ jobs:
 
       - name: Run Tests
         run: |
-          GITHUB_CI=true cargo test --all-features \
+          GITHUB_CI=true RUST_BACKTRACE=1 cargo test --all-features \
             -p std-shims \
             -p zalloc \
             -p serai-db \