Test renderReadmeFile (#23185)

Add test coverage to the important features of
[`routers.web.repo.renderReadmeFile`](https://github.com/go-gitea/gitea/blob/067b0c2664d127c552ccdfd264257caca4907a77/routers/web/repo/view.go#L273);
namely that:

- it can handle looking in docs/, .gitea/, and .github/
- it can handle choosing between multiple competing READMEs
- it prefers the localized README to the markdown README to the
plaintext README
- it can handle broken symlinks when processing all the options
- it uses the name of the symlink, not the name of the target of the
symlink

models/db/iterate_test.go

@@ -25,7 +25,7 @@ func TestIterate(t *testing.T) {
 		return nil
 	})
 	assert.NoError(t, err)
-	assert.EqualValues(t, 83, repoCnt)
+	assert.EqualValues(t, 84, repoCnt)
 
 	err = db.Iterate(db.DefaultContext, nil, func(ctx context.Context, repoUnit *repo_model.RepoUnit) error {
 		reopUnit2 := repo_model.RepoUnit{ID: repoUnit.ID}

models/db/list_test.go

@@ -35,11 +35,11 @@ func TestFind(t *testing.T) {
 	var repoUnits []repo_model.RepoUnit
 	err := db.Find(db.DefaultContext, &opts, &repoUnits)
 	assert.NoError(t, err)
-	assert.EqualValues(t, 83, len(repoUnits))
+	assert.EqualValues(t, 84, len(repoUnits))
 
 	cnt, err := db.Count(db.DefaultContext, &opts, new(repo_model.RepoUnit))
 	assert.NoError(t, err)
-	assert.EqualValues(t, 83, cnt)
+	assert.EqualValues(t, 84, cnt)
 
 	repoUnits = make([]repo_model.RepoUnit, 0, 10)
 	newCnt, err := db.FindAndCount(db.DefaultContext, &opts, &repoUnits)