feat: replace deprecated readfp method in config parser lib (#401)

This PR contains changes suggested by Yevhen Chypachenko.

This is the original PR - #400.

Author: sgoral-splunk

.github/workflows/build-test-release.yml

@@ -76,6 +76,8 @@ jobs:
           - "3.9"
           - "3.10"
           - "3.11"
+          - "3.12"
+          - "3.13"
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5

solnlib/splunkenv.py

@@ -309,7 +309,7 @@ def get_conf_stanzas(conf_name: str) -> dict:
 
     parser = ConfigParser(**{"strict": False})
     parser.optionxform = str
-    parser.readfp(StringIO(out))
+    parser.read_file(StringIO(out))
 
     out = {}
     for section in parser.sections():