fix(history): coerce version to string (#298)

The changes in #297 mistakenly omitted coercing the return value to a
string. This resulted in errors like:
"can only concatenate str (not "VersionInfo") to str"

Add test case asserting it's type str

semantic_release/history/__init__.py

@@ -175,7 +175,7 @@ def get_new_version(current_version: str, level_bump: str) -> str:
     if not level_bump:
         logger.debug("No bump requested, returning input version")
         return current_version
-    return semver.VersionInfo.parse(current_version).next_version(part=level_bump)
+    return str(semver.VersionInfo.parse(current_version).next_version(part=level_bump))
 
 
 @LoggedFunction(logger)

tests/history/test_version.py

@@ -72,6 +72,7 @@ def test_major_bump(self):
         assert get_new_version("10.1.0", "major") == "11.0.0"
 
     def test_minor_bump(self):
+        assert type(get_new_version("0.0.0", "minor")) is str
         assert get_new_version("0.0.0", "minor") == "0.1.0"
         assert get_new_version("1.2.0", "minor") == "1.3.0"
         assert get_new_version("1.2.1", "minor") == "1.3.0"