GH Actions: add a basic spellcheck CI check

Follow up on PR 2472 - safeguarding that no new typos get introduced.

Notes:
* The "Typos" tool is known for having a low false positive ratio and being aware of code contexts. However, this also means, it may at times miss some things.
    When selecting it, I deemed the low false positive ratio more important.
* The language has been set to `en-US` as that's the language predominantly used for the WordPress documentation.
    This does mean that various phrases using `en-GB` spelling will need to be fixed/updated.

Ref: https://github.com/crate-ci/typos

Author: jrfnl

.github/workflows/basic-qa.yml

@@ -254,3 +254,15 @@ jobs:
 
       - name: Run PHPStan
         run: phpstan analyse
+
+  typos-check:
+    name: "Find typos"
+
+    runs-on: "ubuntu-latest"
+
+    steps:
+      - name: "Checkout"
+        uses: "actions/checkout@v4"
+
+      - name: "Search for misspellings"
+        uses: "crate-ci/typos@v1"

_typos.toml

@@ -0,0 +1,24 @@
+[files]
+extend-exclude = [
+    "WordPress/Tests/*/*.inc",
+    "WordPress/Tests/*/*.fixed",
+    "WordPress/Tests/*/*.css",
+    "WordPress/Tests/*/*.js",
+]
+ignore-hidden = true
+
+[default]
+locale = "en-us"
+check-filename = true
+extend-ignore-identifiers-re = [
+    # Renaming these (function/array key) names would be a BC-break.
+    'analyse_implode',
+    'analyse_sprintf',
+    'cachable',
+    'is_targetted_token',
+    # These are search targets for sniffs, can't be helped.
+    'avail_post_stati',
+    'url_is_accessable_via_ssl',
+]
+
+[default.extend-words]