Make non-numeric non-empty FORCE_COLOR truthy (#14140)

Fixes #14139

Author: hauntsaninja

mypy/util.py

@@ -520,7 +520,11 @@ def parse_gray_color(cup: bytes) -> str:
 
 
 def should_force_color() -> bool:
-    return bool(int(os.getenv("MYPY_FORCE_COLOR", os.getenv("FORCE_COLOR", "0"))))
+    env_var = os.getenv("MYPY_FORCE_COLOR", os.getenv("FORCE_COLOR", "0"))
+    try:
+        return bool(int(env_var))
+    except ValueError:
+        return bool(env_var)
 
 
 class FancyFormatter: