(chore) bump version to v1.28.0 for release #998

Job	Run time
Docker	19s
Compatibility	26s
Pydantic V1	17s
ubuntu-latest - python 3.8 - Lint	15s
ubuntu-latest - python 3.8 - Type check	21s
ubuntu-latest - python 3.8 - Unit tests	1m 11s
ubuntu-latest - python 3.8 - Doc tests	1m 33s
ubuntu-latest - python 3.8 - Doc tests (B)	1m 27s
ubuntu-latest - python 3.8 - Images	43s
ubuntu-latest - python 3.8 - Jobs	20s
ubuntu-latest - python 3.8 - Experiments	40s
ubuntu-latest - python 3.8 - Datasets	58s
ubuntu-latest - python 3.8 - Sweep example	39s
ubuntu-latest - python 3.8 - Build	19s
ubuntu-latest - python 3.8 - Style	16s
ubuntu-latest - python 3.8 - Docs	31s
Release	0s
	10m 15s

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