git: fix cachemap bug on sha identifier

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

source/git/gitsource.go

@@ -171,7 +171,7 @@ func (gs *gitSourceHandler) CacheKey(ctx context.Context, index int) (string, bo
 
 	if isCommitSHA(ref) {
 		gs.cacheKey = ref
-		return ref, false, nil
+		return ref, true, nil
 	}
 
 	gitDir, unmountGitDir, err := gs.mountRemote(ctx, remote)

source/git/gitsource_test.go

@@ -167,8 +167,9 @@ func testFetchBySHA(t *testing.T, keepGitDir bool) {
 	g, err := gs.Resolve(ctx, id)
 	require.NoError(t, err)
 
-	key1, _, err := g.CacheKey(ctx, 0)
+	key1, done, err := g.CacheKey(ctx, 0)
 	require.NoError(t, err)
+	require.True(t, done)
 
 	require.Equal(t, 40, len(key1))