Fix stubname equal suffix in wide to long function
- [x] closes #46939(Replace xxxx with the GitHub issue number)
- [x] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature. (Will add after review)

As `pandas` allows an index in a multiindex and a column to have the same name, I think it's reasonable to allow stubname equal suffix.

However, I think the root cause is in the `melt` function. It's stated in the docstring that

```
    value_name : scalar, default 'value'
        Name to use for the 'value' column, can't be an existing column label.
```

But if `value_name == var_name`, illogical result is returned. Example:

```
df = pd.DataFrame(
    {
        "A": {0: "a", 1: "b", 2: "c"},
        "B": {0: 1, 1: 3, 2: 5},
        "C": {0: 2, 1: 4, 2: 6},
    }
)
pd.melt(
    df,
    id_vars=["A"],
    value_vars=["B"],
    var_name="myVarname",
    value_name="myVarname",
)
```

Result:

![image](https://github.com/pandas-dev/pandas/assets/25203655/e4c01d61-8c44-4e89-a858-c811cc722ed4)

I think it's more reasonable to also raise an error if `value_name == var_name` in `melt`
Hi @mroeschke, can you take a look at this PR, please? It should be ready for review. hi @datapythonista, thank you for the review. I also force pushed to the branch because I noticed that you also didn't make any comment on the actual content of the PR. Now this PR should be ready for review. Thanks for the update here @tqa236. The fix you implemented seems a hack, not the proper fix. You should identify what's causing the exception, which seem kind of unrelated, and fix that. Please let me know if you want to have a look more in detail to the actual problem, otherwise we can close this PR. thank you for taking a look @datapythonista, unfortunately it's been a year and the context of this issue is no longer fresh in my mind. Let's close this PR.