fix(typing): Using correct typing for param_hint

The typing of `param_hint` between `BadParameter`, `MissingParameter` and `_join_param_hints` was different.
The firsts only allowed for a `str` where the later also accept a sequence of `str`.

Fixes #2777

Author: FirelightFlagboy

src/click/exceptions.py

@@ -115,7 +115,7 @@ def __init__(
         message: str,
         ctx: Context | None = None,
         param: Parameter | None = None,
-        param_hint: str | None = None,
+        param_hint: cabc.Sequence[str] | str | None = None,
     ) -> None:
         super().__init__(message, ctx)
         self.param = param
@@ -151,15 +151,15 @@ def __init__(
         message: str | None = None,
         ctx: Context | None = None,
         param: Parameter | None = None,
-        param_hint: str | None = None,
+        param_hint: cabc.Sequence[str] | str | None = None,
         param_type: str | None = None,
     ) -> None:
         super().__init__(message or "", ctx, param, param_hint)
         self.param_type = param_type
 
     def format_message(self) -> str:
         if self.param_hint is not None:
-            param_hint: str | None = self.param_hint
+            param_hint: cabc.Sequence[str] | str | None = self.param_hint
         elif self.param is not None:
             param_hint = self.param.get_error_hint(self.ctx)  # type: ignore
         else: