remove 3.7 testing (#179)

3.7 is EOL, and setup-python no longer supports it. WE need to continue to support it for a little while; however, we have to stop testing it so that PR builds can pass

Author: mshafer-NI

.github/workflows/PR.yml

@@ -46,7 +46,7 @@ jobs:
     strategy:
       matrix:
         os: [macos-latest, windows-latest, ubuntu-latest]
-        python-version: [3.7, 3.8, 3.9, '3.10', 3.11, 3.12]
+        python-version: [3.8, 3.9, '3.10', 3.11, 3.12]
     steps:
       - uses: actions/checkout@v2
       - uses: actions/setup-python@v2