Make CI use a dummy password hasher for all tests (#22983)

During the recent hash algorithm change it became clear that the choice
of password hash algorithm plays a role in the time taken for CI to run.

Therefore as attempt to improve CI we should consider using a dummy
hashing algorithm instead of a real hashing algorithm.

This PR creates a dummy algorithm which is then set as the default
hashing algorithm during tests that use the fixtures. This hopefully
will cause a reduction in the time it takes for CI to run.

---------

Signed-off-by: Andrew Thornton <art27@cantab.net>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/auth/password/hash/dummy_test.go

@@ -0,0 +1,25 @@
+// Copyright 2023 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package hash
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestDummyHasher(t *testing.T) {
+	dummy := &PasswordHashAlgorithm{
+		PasswordSaltHasher: NewDummyHasher(""),
+		Specification:      "dummy",
+	}
+
+	password, salt := "password", "ZogKvWdyEx"
+
+	hash, err := dummy.Hash(password, salt)
+	assert.Nil(t, err)
+	assert.Equal(t, hash, salt+":"+password)
+
+	assert.True(t, dummy.VerifyPassword(password, hash, salt))
+}