Use t.TempDir for SQLite databases, so tests don't rip out each others databases (#2950)

This should hopefully finally fix issues about `disk I/O error` as seen
[here](https://gitlab.alpinelinux.org/alpine/aports/-/jobs/955030/raw)

Hopefully this will also fix `SSL accept attempt failed` issues by
disabling HTTP keep alives when generating a config for CI.

test/db.go

@@ -22,6 +22,7 @@ import (
 	"os"
 	"os/exec"
 	"os/user"
+	"path/filepath"
 	"testing"
 
 	"github.com/lib/pq"
@@ -103,13 +104,10 @@ func currentUser() string {
 // TODO: namespace for concurrent package tests
 func PrepareDBConnectionString(t *testing.T, dbType DBType) (connStr string, close func()) {
 	if dbType == DBTypeSQLite {
-		// this will be made in the current working directory which namespaces concurrent package runs correctly
-		dbname := "dendrite_test.db"
+		// this will be made in the t.TempDir, which is unique per test
+		dbname := filepath.Join(t.TempDir(), "dendrite_test.db")
 		return fmt.Sprintf("file:%s", dbname), func() {
-			err := os.Remove(dbname)
-			if err != nil {
-				t.Fatalf("failed to cleanup sqlite db '%s': %s", dbname, err)
-			}
+			t.Cleanup(func() {}) // removes the t.TempDir
 		}
 	}
 
@@ -176,7 +174,7 @@ func WithAllDatabases(t *testing.T, testFn func(t *testing.T, db DBType)) {
 	for dbName, dbType := range dbs {
 		dbt := dbType
 		t.Run(dbName, func(tt *testing.T) {
-			//tt.Parallel()
+			tt.Parallel()
 			testFn(tt, dbt)
 		})
 	}