Fix type piracies in minimum, maximum, extrema. See #1990

[joa-quim]

Also fix another type piracy with the 'names' method.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 36.84211% with 12 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (master@5b9e8d1). Learn more about missing BASE report.
⚠️ Report is 5 commits behind head on master.

Files with missing lines	Patch %	Lines
src/gmt_types.jl	0.00%	5 Missing ⚠️
src/gmt_main.jl	0.00%	3 Missing ⚠️
src/utils.jl	70.00%	3 Missing ⚠️
src/gdal_utils.jl	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master    #1993   +/-   ##
=========================================
  Coverage          ?   85.09%           
=========================================
  Files             ?      191           
  Lines             ?    29048           
  Branches          ?        0           
=========================================
  Hits              ?    24718           
  Misses            ?     4330           
  Partials          ?        0           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.