[Cargo]: Bump serde from 1.0.204 to 1.0.207 in the core group

[dependabot]

Bumps the core group with 1 update: serde.

Updates serde from 1.0.204 to 1.0.207

Release notes

Sourced from serde's releases.

v1.0.207

• Improve interactions between flatten attribute and skip_serializing/skip_deserializing (#2795, thanks @​Mingun)

v1.0.206

• Improve support for flatten attribute inside of enums (#2567, thanks @​Mingun)

v1.0.205

• Use serialize_entry instead of serialize_key + serialize_value when serialize flattened newtype enum variants (#2785, thanks @​Mingun)
• Avoid triggering a collection_is_never_read lint in the deserialization of enums containing flattened fields (#2791)

Commits

• 1b4da41 Release 1.0.207
• f61d452 Touch up PR 2795
• f986609 Merge pull request #2795 from Mingun/has-flatten-rework
• 77a6a9d Take into account only not skipped flatten fields when choose serialization form
• 547d843 Remove dead code - serialize_struct_as_map always called when cattrs.has_flat...
• 005cb84 Fail with an understandable message is number of fields for serialization is ...
• fd5b5e9 Correctly calculate has_flatten attribute in all cases for deserialization
• 0647a7c Fix creating and filling a collections that was not read
• 85c73ef Release 1.0.206
• 5ba1796 Resolve doc_markdown pedantic lint on regression test function
• Additional commits viewable in compare view

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