Adjust version test for new format in version file

The new code matches what is done in cisagov/skeleton-docker:
-
https://github.com/cisagov/skeleton-docker/blob/722507bd51e06538f1f85b659df616ca7ca7fcbd/tests/conftest.py#L41-L46
- https://github.com/cisagov/skeleton-docker/blob/722507bd51e06538f1f85b659df616ca7ca7fcbd/tests/container_test.py#L61-L68

Co-authored-by: Nick M <50747025+mcdonnnj@users.noreply.github.com>

Author: jsf9k

tests/test_version.py

@@ -10,16 +10,20 @@
 VERSION_FILE = "src/version.txt"
 
 
+@pytest.fixture(scope="session")
+def project_version():
+    """Return the version of the project."""
+    with open(VERSION_FILE) as f:
+        project_version = f.read().strip()
+    return project_version
+
+
 @pytest.mark.skipif(
     GITHUB_RELEASE_TAG in [None, ""],
     reason="this is not a release (GITHUB_RELEASE_TAG not set)",
 )
-def test_release_version():
+def test_release_version(project_version):
     """Verify that release tag version agrees with the module version."""
-    pkg_vars = {}
-    with open(VERSION_FILE) as f:
-        exec(f.read(), pkg_vars)  # nosec
-    project_version = pkg_vars["__version__"]
     assert (
         GITHUB_RELEASE_TAG == f"v{project_version}"
     ), "GITHUB_RELEASE_TAG does not match the project version"