Fix dtypes in get_pvgis_tmy when outputformat='epw'

[AdamRJensen]

• Closes Error with using PVGIS weather data (zenith conversion in airmass?) #2399
• I am familiar with the contributing guidelines
• Tests added
• Updates entries in docs/sphinx/source/reference for API changes.
• Adds description and name entries in the appropriate "what's new" file in docs/sphinx/source/whatsnew for all changes. Includes link to the GitHub Issue with :issue:`num` or this Pull Request with :pull:`num`. Includes contributor name and/or GitHub username (link with :ghuser:`user`).
• New code is fully documented. Includes numpydoc compliant docstrings, examples, and comments where necessary.
• Pull request is nearly complete and ready for detailed review.
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This PR fixes incorrect dtypes returned by get_pvgis_tmy when outputformat='epw' and coerce_year is not None.

[kandersolar]

Suggested change

	new_tmy_data = \ # GH 2399
	new_tmy_data.astype(dtype=dict(zip(tmy_data.columns, tmy_data.dtypes)))
	# GH 2399
	new_tmy_data = \
	new_tmy_data.astype(dtype=dict(zip(tmy_data.columns, tmy_data.dtypes)))

Sorry my last suggestion broke this :(