Add FLEPI_PATH to GH action, fix Jinja2 loader

* Export `$FLEPI_PATH` in the GH action before running tests to run the
  unit tests for `get_cluster_info`.
* Attempt to fix Jinja2 lader issue by falling back to a file system
  loader if a package loader fails.

.github/workflows/gempyor-ci.yml

@@ -43,6 +43,7 @@ jobs:
         shell: bash
       - name: Run gempyor tests
         run: |
+          export FLEPI_PATH=$(pwd)
           cd flepimop/gempyor_pkg
           pytest --exitfirst
         shell: bash

flepimop/gempyor_pkg/src/gempyor/_jinja.py

@@ -14,11 +14,18 @@
 from tempfile import mkstemp
 from typing import Any
 
-from jinja2 import Environment, PackageLoader, Template
+from jinja2 import Environment, FileSystemLoader, PackageLoader, Template
 
 
 # Globals
-_jinja_environment = Environment(loader=PackageLoader("gempyor", "templates"))
+try:
+    _jinja_environment = Environment(loader=PackageLoader("gempyor", "templates"))
+except ValueError:
+    from os.path import dirname
+
+    _jinja_environment = Environment(
+        loader=FileSystemLoader(dirname(__file__) + "/templates")
+    )
 
 
 # Functions