Build fails on aarch64 after error: Assignment: Cannot convert from `int64' to `time_t'

### What Happened?

I'm building calendar on an aarch64 environment. Compiling fails after these messages:
```
libgdata.vapi:2038.3-2038.27: warning: Creation method of abstract class cannot be public.
public Parsable.from_json (GLib.Type parsable_type, string json, int length) throws GLib.Error;
^^^^^^^^^^^^^^^^^^^^^^^^^
libgdata.vapi:2041.3-2041.26: warning: Creation method of abstract class cannot be public.
public Parsable.from_xml (GLib.Type parsable_type, string xml, int length) throws GLib.Error;
^^^^^^^^^^^^^^^^^^^^^^^^
../core/Services/Calendar/Util/ECalComponent.vala:75.16-75.25: error: Assignment: Cannot convert from `int64' to `time_t'
time_t start_unix = start_time.as_timet_with_zone (system_timezone);
^^^^^^^^^^
../core/Services/Calendar/Util/ECalComponent.vala:76.16-76.23: error: Assignment: Cannot convert from `int64' to `time_t'
time_t end_unix = end_time.as_timet_with_zone (system_timezone);
^^^^^^^^
../core/Services/Calendar/Util/ICalTime.vala:57.20-57.77: warning: `GLib.TimeZone.new' has been deprecated since 2.68. Use TimeZone.identifier
../core/Services/Calendar/Util/ICalTime.vala:61.20-61.43: warning: `GLib.TimeZone.new' has been deprecated since 2.68. Use TimeZone.identifier
Compilation failed: 2 error(s), 4 warning(s)
ninja: subcommand failed
```

### Steps to Reproduce

1. Chroot into an aarch64 environment
2. Install all build-tools and dependencies listed in the README.md
3. Clone the repo
4. cd into the clone
5. optional: checkout 6.1.0
5. meson build --prefix=/usr
6. cd build
7. ninja

Step 7 fails after the messages mentioned above.

### Expected Behavior

I expected to end up with an executable of calendar for aarch64 architecture.

### OS Version

Other Linux

### Software Version

Latest release (I have run all updates)

### Log Output

_No response_

### Hardware Info

The environment is an aarch64 environment with Alpine Linux, created using qemu, hosted on a amd64 machine.