ci: Run tests using PostgreSQL database and mock (#49)

* ci: Run tests using PostgreSQL database and mock

This allows us to use the mock database for quick iterative testing,
and have confidence from CI using a real PostgreSQL database.

PostgreSQL tests are only ran on Linux. They are *really* slow on MacOS
and Windows runners, and don't provide much additional confidence.

* Only run PostgreSQL tests once for speed

* Fix race condition of log after close

Not all resources were cleaned up immediately after a peer connection was
closed. DataChannels could have a goroutine exit after Close() prior to this.

* Fix comment

.github/workflows/coder.yaml

@@ -149,11 +149,19 @@ jobs:
 
       - run: go install gotest.tools/gotestsum@latest
 
-      - run:
+      - name: Test with Mock Database
+        run:
           gotestsum --jsonfile="gotests.json" --packages="./..." --
           -covermode=atomic -coverprofile="gotests.coverage" -timeout=3m
           -count=3 -race -parallel=2
 
+      - name: Test with PostgreSQL Database
+        if: runner.os == 'Linux'
+        run:
+          DB=true gotestsum --jsonfile="gotests.json" --packages="./..." --
+          -covermode=atomic -coverprofile="gotests.coverage" -timeout=3m
+          -count=1 -race -parallel=2
+
       - uses: codecov/codecov-action@v2
         with:
           token: ${{ secrets.CODECOV_TOKEN }}