ci: spelling: remove branch / tag filtering (#5126)

This repository tends to use `/`s in branch names.
Unfortunately, `branch: "*"` at present only matches a single
level, which means it would match a branch named `foo` but not `bar/foo`.

Given that I don't think this repository is actively using tags,
and given that the general cost for the spell checker isn't particularly
high, it's better to remove the filtering so that all branches get
checked.

Worst case, a branch that is also tagged and has spelling errors
will get two comments complaining about those spelling errors.

Author: jsoref

.github/workflows/spelling.yml

@@ -1,10 +1,6 @@
 name: Spell checking
 on:
   push:
-    branches:
-      - "*"
-    tags-ignore:
-      - "*"
   schedule:
     # * is a special character in YAML so you have to quote this string
     - cron: '15 * * * *'