GitLab's token doesn't work if GitHub's token is set

[grzesjam]

Expected Behavior

When URL is github.com it uses GITHUB_TOKEN token, and if gitlab.com uses GITLAB_TOKEN token
OR
Have one generic GIT_AUTH_TOKEN used for authentications (with warning its always used for all connections)
OR
Provide GIT_AUTH_TOKEN array and all tokens be checked/matched for access

Actual Behavior

Regardless of URL if GITHUB_TOKEN is set its always used, always auth is returned.

fanal/artifact/remote/git.go

Lines 111 to 132 in f400923

	githubToken := os.Getenv("GITHUB_TOKEN")
	if githubToken != "" {
	auth = &http.BasicAuth{
	Username: gitUsername,
	Password: githubToken,
	}
	return auth
	}
	// Otherwise we check if a GitLab token was provided
	gitlabToken := os.Getenv("GITLAB_TOKEN")
	if gitlabToken != "" {
	auth = &http.BasicAuth{
	Username: gitUsername,
	Password: gitlabToken,
	}
	return auth
	}
	// If no token was provided, we simply return a nil,
	// which will make the request to be unauthenticated
	return nil

Steps to Reproduce the Problem

1. Set dummy/real GITHUB_TOKEN ( export GITHUB_TOKEN="ghp_xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx")
2. Set real GITLAB_TOKEN ( export GITLAB_TOKEN="glpat-xxxxxxxxxxxxxxxxxxxx" )
3. Run remote repo scanning in trivy or any other tool using this library ( trivy repo https://gitlab.com/private-organization/private-repo or trivy repo https://gitlab.com/gitlab-org/gitlab )
4. Get git error: authentication required

Specifications

• Version: trivy - 0.25.0 , fanal - v0.0.0-20220516143651-a81c666fb9b5
• Platform: linux (ubuntu and apline)
• Subsystem: Trivy