github/workflows: Add check for misspelling of "MicroPython".

"MicroPython" is sometimes misspelled as "Micropython".  Add an explicit
check for that as part of CI (note that codespell doesn't consider case
when spelling, hence the need to do it this way).

Signed-off-by: Damien George <damien@micropython.org>

.github/workflows/codespell.yml

@@ -10,4 +10,9 @@ jobs:
     # codespell version should be kept in sync with .pre-commit-config.yml
     - run: pip install --user codespell==2.4.1 tomli
     - run: codespell
-
+    # additionally check for misspelling of "MicroPython"
+    - run: |
+        if git grep -n Micropython -- ":(exclude).github/workflows/codespell.yml"; then
+            echo "Please correct capitalisation of MicroPython on the above lines"
+            exit 1
+        fi