BUG: concat doesn't preserve attrs (as alternative for append deprecated in 1.4)

[MarcoGorelli]

Pandas version checks

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• I have confirmed this bug exists on the latest version of pandas.

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Reproducible Example

import pandas
df1 = pandas.DataFrame({"a": [1]})
df2 = pandas.DataFrame({"a": [2]})
df1.attrs["metadata-xy"] = 42

print(df1.append(df2).attrs)  # keeps the attrs of df1
print(pandas.concat([df1, df2]).attrs)  # no attrs in result

Issue Description

append preserves attrs, but concat doesn't

Originally reported here #35407 (comment)

Expected Behavior

df1.append(df2).attrs and pandas.concat([df1, df2]).attrs should probably match

Installed Versions

Replace this line with the output of pd.show_versions()

[rhshadrach]

There is some discussion on what the behavior should be in #28283, but perhaps it is worthy of an issue on its own.

[asishm]

related #41828

[lithomas1]

I think concat only keeps the attrs only when they match by design. Re-labeling as enhancement.
#41828 (comment)