Deflake unit tests

I was seeing occasional panics with:

panic: close of closed channel
goroutine XXX [running]:
vitess.io/vitess/go/vt/binlog/binlogplayer.(*MockDBClient).ExecuteFetch(0xc000282070, {0xc00005d020, 0x24}, 0x1?)

Signed-off-by: Matt Lord <mattalord@gmail.com>

go/vt/binlog/binlogplayer/mock_dbclient.go

@@ -103,13 +103,13 @@ func NewMockDbaClient(t *testing.T) *MockDBClient {
 // ExpectRequest adds an expected result to the mock.
 // This function should not be called conncurrently with other commands.
 func (dc *MockDBClient) ExpectRequest(query string, result *sqltypes.Result, err error) {
+	dc.expectMu.Lock()
+	defer dc.expectMu.Unlock()
 	select {
 	case <-dc.done:
 		dc.done = make(chan struct{})
 	default:
 	}
-	dc.expectMu.Lock()
-	defer dc.expectMu.Unlock()
 	dc.expect = append(dc.expect, &mockExpect{
 		query:  query,
 		result: result,
@@ -121,13 +121,13 @@ func (dc *MockDBClient) ExpectRequest(query string, result *sqltypes.Result, err
 // queryRE is a regular expression.
 // This function should not be called conncurrently with other commands.
 func (dc *MockDBClient) ExpectRequestRE(queryRE string, result *sqltypes.Result, err error) {
+	dc.expectMu.Lock()
+	defer dc.expectMu.Unlock()
 	select {
 	case <-dc.done:
 		dc.done = make(chan struct{})
 	default:
 	}
-	dc.expectMu.Lock()
-	defer dc.expectMu.Unlock()
 	dc.expect = append(dc.expect, &mockExpect{
 		query:  queryRE,
 		re:     regexp.MustCompile(queryRE),

go/vt/vttablet/tabletmanager/vdiff/framework_test.go

@@ -623,10 +623,10 @@ func (tvde *testVDiffEnv) close() {
 		tstenv.SchemaEngine.Reload(context.Background())
 	}
 	tvde.tablets = nil
-	vdiffenv.vse.Close()
-	vdiffenv.vre.Close()
-	vdiffenv.vde.Close()
-	vdiffenv.dbClient.Close()
+	tvde.vse.Close()
+	tvde.vre.Close()
+	tvde.vde.Close()
+	tvde.dbClient.Close()
 }
 
 func (tvde *testVDiffEnv) addTablet(id int, keyspace, shard string, tabletType topodatapb.TabletType) *fakeTabletConn {