update gh workflow for spellcheck and update requirements.txt

copied from git-intro repository

.github/workflows/spellcheck.yml

@@ -1,24 +1,23 @@
-name: Spelling Errors Check
+name: Spelling Erros Check
 
-on: 
-  push:
-    branches:
-      - 'master'
-      - 'main'
-  pull_request:
+on: [push]
 
 jobs:
   build:
     strategy:
       max-parallel: 2
       matrix:
         os: [ubuntu-latest]
-      
+
     runs-on: ${{ matrix.os }}
 
     steps:
     - uses: actions/checkout@v1
+    - name: Install dependencies
+      run: curl -L https://git.io/misspell | bash
 
-    - uses: codespell-project/actions-codespell@master
-      with:
-        ignore_words_list: carpentries, agre
+    # This will return an exit code of 2, thus triggering a failed build
+    - name: Test spelling errors
+      shell: bash
+      run: |
+        bin/misspell -error *

requirements.txt

@@ -1,7 +1,8 @@
 Sphinx
 sphinx_rtd_theme
+sphinx_rtd_theme_ext_color_contrast
 myst_nb
+# Remove once new sphinx-copybutton is released ( > 0.5.0)
+git+https://github.com/rkdarst/sphinx-copybutton.git@exclude-unselectable-3
 sphinx-lesson
-sphinx_rtd_theme_ext_color_contrast
 https://github.com/coderefinery/sphinx-coderefinery-branding/archive/master.zip
-https://github.com/rkdarst/sphinx-contrib-youtube/archive/live.zip