NEP29: Test PyGMT on NumPy 1.23 and 1.21 (#2057)

* NEP29: Test PyGMT on NumPy 1.23

Bumps [numpy](https://github.com/numpy/numpy) from 1.22.4 to 1.23.2.
- [Release notes](https://github.com/numpy/numpy/releases)
- [Changelog](https://github.com/numpy/numpy/blob/v1.23.0/doc/changelog/1.23.0-changelog.rst)
- [Commits](numpy/numpy@v1.22.4...v1.23.2)

* Set minimum NumPy version to 1.21 for CI tests

Bypass issue with `TypeError: <class 'numpy.typing._dtype_like._SupportsDType'> is not a generic class` reported in pydata/xarray#6818.

Author: weiji14

.github/workflows/ci_tests.yaml

@@ -40,14 +40,14 @@ jobs:
             isDraft: true
           - os: windows-latest
             isDraft: true
-        # Pair Python 3.8 with NumPy 1.20 and Python 3.10 with NumPy 1.22
-        # Only install optional packages on Python 3.10/NumPy 1.22
+        # Pair Python 3.8 with NumPy 1.21 and Python 3.10 with NumPy 1.23
+        # Only install optional packages on Python 3.10/NumPy 1.23
         include:
           - python-version: '3.8'
-            numpy-version: '1.20'
+            numpy-version: '1.21'
             optional-packages: ''
           - python-version: '3.10'
-            numpy-version: '1.22'
+            numpy-version: '1.23'
             optional-packages: 'geopandas ipython'
     timeout-minutes: 30
     defaults: