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How to resolve a "ValueError: dimension 't' already exists as a scalar variable" arising when I am using xarray.Dataset.assign_coords()?

~~I have the following `xarray.Dataset`:~~
`d: <xarray.Dataset>`
~~`Dimensions: (x: 79, y: 63, t: 1)`~~
~~`Coordinates:`~~
~~`* x (x) float64 0.9412 1.882 2.824 3.765 ... 71.53 72.47 73.41 74.35`~~
~~` * y (y) float64 59.29 58.35 57.41 56.47 ... 3.765 2.824 1.882 0.9412`~~
~~`* t (t) int32 0`~~
~~`Data variables:`~~
u (x, y, t) float64 0.0 0.0 0.0 0.0 0.0 0.0 ... 0.0 0.0 0.0 0.0 0.0
v (x, y, t) float64 -0.0 -0.0 -0.0 -0.0 -0.0 ... -0.0 -0.0 -0.0 -0.0
chc (x, y, t) float64 1.0 1.0 1.0 1.0 1.0 1.0 ... 1.0 1.0 1.0 1.0 1.0
`Attributes: (2)`
~~I'm trying to assign new values to the coordinate `t` using `.assign_coords()`:~~
`d = d.assign_coords(t = 0.123)`
~~I receive an error: `ValueError: dimension 't' already exists as a scalar variable`~~
~~How to resolve the error and assign a new value to the `t` coordinate?~~
~~-------------------~~
I have tried the solutions to the similar problems posted on StackOverflow, such as 1) `assign_coords` is not an inplace operation, 2) recreate `t` as a coordinate and then assign the value to it, 3) change the type of `t` to `float`. Also, I suspected that the asterisk next to the name of my coordinate `t` has something to do with the error. But I don't know what the asterisk means, I could only find that it is a reference to something called "proper coordinate".
~~P.S. I am sorry for the formatting of my code: I didn't know how to code-format a chunk of code spanning several lines.~~

I have the following [xarray](https://docs.xarray.dev/en/stable/index.html) `Dataset`:
```
d: <xarray.Dataset>
Dimensions: (x: 79, y: 63, t: 1)
Coordinates:
* x (x) float64 0.9412 1.882 2.824 3.765 ... 71.53 72.47 73.41 74.35
* y (y) float64 59.29 58.35 57.41 56.47 ... 3.765 2.824 1.882 0.9412
* t (t) int32 0
Data variables:
u (x, y, t) float64 0.0 0.0 0.0 0.0 0.0 0.0 ... 0.0 0.0 0.0 0.0 0.0
v (x, y, t) float64 -0.0 -0.0 -0.0 -0.0 -0.0 ... -0.0 -0.0 -0.0 -0.0
chc (x, y, t) float64 1.0 1.0 1.0 1.0 1.0 1.0 ... 1.0 1.0 1.0 1.0 1.0
Attributes: (2)
```
When I try to assign new values to the coordinate `t`, using `d = d.assign_coords(t = 0.123)`, I receive an error:
`ValueError: dimension 't' already exists as a scalar variable`
How can I resolve the error and assign a new value to the `t` coordinate?
I have tried the solutions to the similar problems posted on Stack Overflow, such as
* `assign_coords` is not an inplace operation
* recreate `t` as a coordinate and then assign the value to it
* change the type of `t` to `float`
I suspect that the asterisk next to the name of my coordinate `t` has something to do with the error. But I don't understand what it means; I could only find that it is a reference to something called "proper coordinate".

python xarray

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