Make setuptools check on CI more precise

This checks for setuptools as a full word at the very beginning of
a line of output from "pip freeze --all", to:

- Avoid the unlikely but possible case that setuptools is absent
  while something besides setuptools has "setuptools" in its line.

- Prevent "setuptools" from being passed to install multiple times.
  This causes no problems -- it's still only installed/upgraded at
  most once -- but it was making the GitHub Actions log confusing
  on Cygwin. (It could happen on other platforms, but hasn't been.)

.github/workflows/cygwin-test.yml

@@ -63,7 +63,7 @@ jobs:
     - name: Update PyPA packages
       run: |
         # Get the latest pip, wheel, and prior to Python 3.12, setuptools.
-        python -m pip install -U pip $(pip freeze --all | grep -oF setuptools) wheel
+        python -m pip install -U pip $(pip freeze --all | grep -ow ^setuptools) wheel
 
     - name: Install project and test dependencies
       run: |

.github/workflows/pythonpackage.yml

@@ -56,7 +56,7 @@ jobs:
     - name: Update PyPA packages
       run: |
         # Get the latest pip, wheel, and prior to Python 3.12, setuptools.
-        python -m pip install -U pip $(pip freeze --all | grep -oF setuptools) wheel
+        python -m pip install -U pip $(pip freeze --all | grep -ow ^setuptools) wheel
 
     - name: Install project and test dependencies
       run: |