Upgrade to numpy 1.21 to prepare for Python 3.10

Fixes opencv#525

Numpy's Python 3.10 statements at https://github.com/numpy/numpy/releases

Python 3.10 release candidate 2
https://www.python.org/downloads/release/python-3100rc2
https://github.com/actions/python-versions/releases --> 3.10.0-rc.2

Author: cclauss

Diff for: pyproject.toml

@@ -3,8 +3,9 @@ requires = [
   "setuptools", "wheel", "scikit-build", "cmake", "pip",
   "numpy==1.13.3; python_version=='3.6' and platform_machine != 'aarch64' and platform_machine != 'arm64'",
   "numpy==1.19.3; python_version>='3.6' and sys_platform == 'linux' and platform_machine == 'aarch64'",
-  "numpy==1.21.0; python_version>='3.6' and sys_platform == 'darwin' and platform_machine == 'arm64'",
+  "numpy==1.21.2; python_version>='3.6' and sys_platform == 'darwin' and platform_machine == 'arm64'",
   "numpy==1.14.5; python_version=='3.7' and platform_machine != 'aarch64' and platform_machine != 'arm64'",
   "numpy==1.17.3; python_version=='3.8' and platform_machine != 'aarch64' and platform_machine != 'arm64'",
-  "numpy==1.19.3; python_version>='3.9' and platform_machine != 'aarch64' and platform_machine != 'arm64'"
+  "numpy==1.19.3; python_version>='3.9' and platform_machine != 'aarch64' and platform_machine != 'arm64'",
+  "numpy==1.21.2; python_version>='3.10' and platform_machine != 'aarch64' and platform_machine != 'arm64'"
 ]