Use type refinement for post_caption

Author: ryanlua

src/instawebhooks/__main__.py

@@ -145,16 +145,18 @@ async def create_embed(post: Post):
     profile_pic_file = File(io.BytesIO(profile_pic_bytes), "profile_pic.webp")
 
     # Format the post caption with clickable links for mentions and hashtags
-    post_caption = re.sub(
-        r"#([a-zA-Z0-9]+\b)",
-        r"[#\1](https://www.instagram.com/explore/tags/\1)",
-        post.caption,
-    )
-    post_caption = re.sub(
-        r"@([a-zA-Z0-9_]+\b)",
-        r"[@\1](https://www.instagram.com/\1)",
-        post_caption,
-    )
+    post_caption = post.caption
+    if post_caption is str:
+        post_caption = re.sub(
+            r"#([a-zA-Z0-9]+\b)",
+            r"[#\1](https://www.instagram.com/explore/tags/\1)",
+            post_caption,
+        )
+        post_caption = re.sub(
+            r"@([a-zA-Z0-9_]+\b)",
+            r"[@\1](https://www.instagram.com/\1)",
+            post_caption,
+        )
 
     embed = Embed(
         color=13500529,