Expose tasks with dates as events in subscribed calendar

Remark: The link to issue template as shown in Contributing.md is throwing a 404 error.

Steps to reproduce

1. Create a calendar with tasks or a task list with the task app.
2. Add calendar entries and tasks which are shown in Nextclouds calendar app
3. Export the calendar and copy the subscription link
4. Import/Subscribe to the calendar in a third party app (here: Fastmail and iOS calendar app and Google calendar)

Expected behaviour

The calendar entries and the tasks should appear in the subscribed calendar

Actual behaviour

The calendar entries appear but the tasks are not shown

Server configuration

Operating system:
Linux 5.4.0-144-generic nextcloud/tasks#161-Ubuntu SMP Fri Feb 3 14:49:04 UTC 2023 x86_64

Web server:
nginx/1.18.0 (fpm-fcgi)

Database:
mysql 10.5.19

PHP version:
8.0.28

Nextcloud version: (see Nextcloud admin page)
25.0.5 - 25.0.5.1

Tasks version: (see Nextcloud apps page)
0.14.5

Updated from an older Nextcloud or fresh install:
Fresh install

Signing status:
???

No errors have been found.

List of activated apps:

 - activity: 2.17.0
 - calendar: 4.3.3
 - circles: 25.0.0
 - cloud_federation_api: 1.8.0
 - comments: 1.15.0
 - contacts: 5.2.0
 - contactsinteraction: 1.6.0
 - dashboard: 7.5.0
 - dav: 1.24.0
 - deck: 1.8.3
 - federatedfilesharing: 1.15.0
 - federation: 1.15.0
 - files: 1.20.1
 - files_pdfviewer: 2.6.0
 - files_rightclick: 1.4.0
 - files_sharing: 1.17.0
 - files_trashbin: 1.15.0
 - files_versions: 1.18.0
 - firstrunwizard: 2.14.0
 - groupfolders: 13.1.2
 - logreader: 2.10.0
 - lookup_server_connector: 1.13.0
 - nextcloud_announcements: 1.14.0
 - notifications: 2.13.1
 - notify_push: 0.6.2
 - oauth2: 1.13.0
 - password_policy: 1.15.0
 - photos: 2.0.1
 - privacy: 1.9.0
 - provisioning_api: 1.15.0
 - recommendations: 1.4.0
 - related_resources: 1.0.4
 - settings: 1.7.0
 - sharebymail: 1.15.0
 - support: 1.8.0
 - survey_client: 1.13.0
 - systemtags: 1.15.0
 - tasks: 0.14.5
 - text: 3.6.0
 - theming: 2.0.1
 - twofactor_backupcodes: 1.14.0
 - twofactor_totp: 7.0.0
 - updatenotification: 1.15.0
 - user_status: 1.5.0
 - viewer: 1.9.0
 - weather_status: 1.5.0
 - workflowengine: 2.7.0

Nextcloud configuration:

{
    "skeletondirectory": "\/var\/www\/html\/themes\/hetzner\/skeleton",
    "simpleSignUpLink.shown": false,
    "memcache.local": "\\OC\\Memcache\\APCu",
    "appstoreurl": "https:\/\/apps.your-storageshare.de",
    "apps_paths": [
        {
            "path": "\/var\/www\/html\/apps",
            "url": "\/apps",
            "writable": false
        },
        {
            "path": "\/var\/www\/html\/custom_apps",
            "url": "\/custom_apps",
            "writable": true
        }
    ],
    "files_external_allow_create_new_local": false,
    "loglevel": 2,
    "log_type": "syslog",
    "updatechecker": false,
    "updater.server.url": "https:\/\/updates.your-storageshare.de",
    "updater.release.channel": "stable",
    "passwordsalt": "***REMOVED SENSITIVE VALUE***",
    "secret": "***REMOVED SENSITIVE VALUE***",
    "datadirectory": "***REMOVED SENSITIVE VALUE***",
    "dbtype": "mysql",
    "version": "25.0.5.1",
    "overwrite.cli.url": "https:\/\/nx37009.your-storageshare.de",
    "dbname": "***REMOVED SENSITIVE VALUE***",
    "dbhost": "***REMOVED SENSITIVE VALUE***",
    "dbport": "",
    "dbtableprefix": "oc_",
    "mysql.utf8mb4": true,
    "dbuser": "***REMOVED SENSITIVE VALUE***",
    "dbpassword": "***REMOVED SENSITIVE VALUE***",
    "installed": true,
    "instanceid": "***REMOVED SENSITIVE VALUE***",
    "default_language": "de",
    "default_locale": "de",
    "default_phone_region": "DE",
    "mail_smtpmode": "smtp",
    "mail_smtpauthtype": "LOGIN",
    "mail_smtphost": "***REMOVED SENSITIVE VALUE***",
    "mail_from_address": "***REMOVED SENSITIVE VALUE***",
    "mail_domain": "***REMOVED SENSITIVE VALUE***",
    "syslog_tag": "nextcloud-nx37009",
    "upgrade.disable-web": true,
    "theme": "hetzner",
    "templatedirectory": "\/var\/www\/html\/core\/skeleton\/Templates\/",
    "enabledPreviewProviders": [
        "OC\\Preview\\PNG",
        "OC\\Preview\\JPEG",
        "OC\\Preview\\GIF",
        "OC\\Preview\\BMP",
        "OC\\Preview\\XBitmap",
        "OC\\Preview\\MP3",
        "OC\\Preview\\TXT",
        "OC\\Preview\\MarkDown",
        "OC\\Preview\\OpenDocument",
        "OC\\Preview\\Krita",
        "OC\\Preview\\HEIC"
    ],
    "activity_expire_days": "31",
    "bulkupload.enabled": false,
    "redis": {
        "host": "***REMOVED SENSITIVE VALUE***",
        "port": "6379",
        "timeout": "1.5",
        "dbindex": "0"
    },
    "filelocking.enabled": true,
    "memcache.locking": "\\OC\\Memcache\\Redis",
    "memcache.distributed": "\\OC\\Memcache\\Redis",
    "trusted_domains": [
        "nx37009.your-storageshare.de",
        "cloud.uwe-gehring.de"
    ],
    "maintenance": false,
    "twofactor_enforced": "true",
    "twofactor_enforced_groups": [],
    "twofactor_enforced_excluded_groups": []
}

Are you using external storage, if yes which one: local/smb/sftp/... no

Are you using encryption: no

Are you using an external user-backend, if yes which one: LDAP/ActiveDirectory/Webdav/... no

Client configuration

Browser:
Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:109.0) Gecko/20100101 Firefox/112.0

CalDAV-clients:
Fastmail
iOS Calendar app
Google calendar

Start by tracing the calendar export and subscription flow described in the reproduction steps, comparing the generated subscription with how tasks appear in the Calendar app. Verify the result with Fastmail, iOS Calendar, or Google Calendar; done means subscribed calendars expose both calendar entries and tasks.