fix(encode): Correct encoding for key with mixed quotes

[coveralls]

Pull Request Test Coverage Report for Build 9978066668

Details

• 33 of 54 (61.11%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.04%) to 67.445%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
crates/toml_edit/src/encode.rs	12	14	85.71%
crates/toml_edit/tests/testsuite/parse.rs	21	40	52.5%
<!--	Total:	33	54	61.11%	-->

Files with Coverage Reduction	New Missed Lines	%
crates/toml/src/de.rs	2	45.9%
<!--	Total:	2		-->

Totals
Change from base Build 9946584060:	-0.04%
Covered Lines:	3727
Relevant Lines:	5526

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💛 - Coveralls