Fixed issues with gcc for apk and updated to python version 3.6

.drone.jsonnet

@@ -19,7 +19,7 @@ local Pipeline(name, image) = {
 };
 
 [
-  Pipeline("python-3-5", "python:3.5"),
+  Pipeline("python-3-6", "python:3.6"),
   Pipeline("python-3-7", "python:3.7"),
   Pipeline("python-3-8", "python:3.8"),
   Pipeline("python-3-9", "python:3.9"),

Jenkinsfile

@@ -33,7 +33,7 @@ pipeline {
                         }
                         steps {
                             sh '''
-                            apk add --no-cache libpq-dev
+                            apk --no-cache add --virtual build-dependencies libpq-dev gcc musl-dev
                             python -m venv ${PY_ENV}
                             source ${PY_ENV}/bin/activate
                             export PATH=${PY_ENV}/bin:${PATH}