build: Update lower bound of click to v8.0.0 (#1958)

* Update lower bound of the supported click versions to v8.0.0 as it
is required to support behavior in PR #1909 due to click v7.x not
setting the type correctly for path type arguments.
   - c.f. #1957 (comment)
* Update tests/constraints.txt to use click==8.0.0.

Author: matthewfeickert

setup.cfg

@@ -36,7 +36,7 @@ include_package_data = True
 python_requires = >=3.7
 install_requires =
     scipy>=1.1.0 # requires numpy, which is required by pyhf and tensorflow
-    click>=7.0  # for console scripts
+    click>=8.0.0  # for console scripts
     tqdm>=4.56.0  # for readxml
     jsonschema>=3.0.0  # for utils
     jsonpatch>=1.15

tests/constraints.txt

@@ -1,6 +1,6 @@
 # core
 scipy==1.1.0
-click==7.0
+click==8.0.0  # c.f. PR #1958, #1909
 tqdm==4.56.0
 jsonschema==3.0.0
 jsonpatch==1.15