Set maximum annotation interval to 60 for some projections

[maxrjones]

Description of proposed changes

Fixes this problem: #4955 (comment)

While the themes branch made this problem worse (i.e., occur for larger maps), even before 6.1.1 small maps (~5cm width) with the Mollweide projection would only have one latitude annotation. This PR makes the maximum auto annotation interval 60 degrees for Mollweide, Hammer, and Eckert 4 projections because the frame slope is too gently at higher latitudes for automatic annotations to be placed.

Command:
gmt basemap -Rg -JW15c -B -png map
Before:

After:

Fixes #

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