Clarified docstring for pixel_ratio for #5813 #1314

Job	Run time
Run pre-commit hooks	16s
UI tests on ubuntu-latest with Python 3.9	2m 17s
Pytest on 3.8, Bokeh 2, ubuntu-latest	30m 30s
Pytest on 3.8, Bokeh 3, ubuntu-latest	31m 39s
Pytest on 3.11, Bokeh 2, ubuntu-latest	35m 27s
Pytest on 3.11, Bokeh 3, ubuntu-latest	34m 5s
Pytest on 3.8, Bokeh 2, macos-latest	39m 34s
Pytest on 3.8, Bokeh 3, macos-latest	38m 41s
Pytest on 3.11, Bokeh 2, macos-latest	36m 58s
Pytest on 3.11, Bokeh 3, macos-latest	37m 54s
Pytest on 3.8, Bokeh 2, windows-latest	50m 28s
Pytest on 3.8, Bokeh 3, windows-latest	53m 42s
Pytest on 3.11, Bokeh 2, windows-latest	42m 39s
Pytest on 3.11, Bokeh 3, windows-latest	52m 49s
	8h 6m 59s

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