CI: Update 3.14 from alpha1 to rc2

cffi 2.0 was published this week and broke support for some 3.14 alpha versions.
This caused a segfault when trying to use python3-cryptography for ecdsa

Author: progval

.github/workflows/test.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         include:
-          - python-version: "3.14.0-alpha.1"
+          - python-version: "3.14.0-rc.2"
             with-opt-deps: true
             runs-on: ubuntu-22.04