Add check for non-executable scripts to "Check Shell" workflow

Since Windows doesn't have the concept of an executable file mode, and shell scripts not considered executable by Linux,
etc. will work fine if a shell is installed (e.g., Git Bash), shell scripts written or worked on by Windows developers
may not be executable. For this reason, it is especially helpful for the CI to do a check on the file mode of the
project's shell scripts, failing if they are not executable.

Author: per1234

Diff for: .github/workflows/check-shell-task.yml

@@ -129,3 +129,19 @@ jobs:
 
       - name: Check formatting
         run: git diff --color --exit-code
+
+  executable:
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v2
+
+      - name: Install Task
+        uses: arduino/setup-task@v1
+        with:
+          repo-token: ${{ secrets.GITHUB_TOKEN }}
+          version: 3.x
+
+      - name: Check for non-executable scripts
+        run: task --silent shell:check-mode

Diff for: Taskfile.yml

@@ -46,6 +46,7 @@ tasks:
       - task: config:check
       - task: general:check-formatting
       - task: check-spelling
+      - task: shell:check-mode
 
   lint:
     desc: Lint all files
@@ -311,6 +312,35 @@ tasks:
         fi
       - shfmt -w .
 
+  # Source: https://github.com/arduino/tooling-project-assets/blob/main/workflow-templates/assets/check-shell-task/Taskfile.yml
+  shell:check-mode:
+    desc: Check for non-executable shell scripts
+    cmds:
+      - |
+        EXIT_STATUS=0
+        while read -r nonExecutableScriptPath; do
+          # The while loop always runs once, even if no file was found
+          if [[ "$nonExecutableScriptPath" == "" ]]; then
+            continue
+          fi
+
+          echo "::error file=${nonExecutableScriptPath}::non-executable script file: $nonExecutableScriptPath";
+          EXIT_STATUS=1
+        done <<<"$(
+          # The odd approach to escaping `.` in the regex is required for windows compatibility because mvdan.cc/sh
+          # gives `\` characters special treatment on Windows in an attempt to support them as path separators.
+          find . \
+            -path ".git" -prune -or \
+            \( \
+              -regextype posix-extended \
+              -regex '.*[.](bash|sh)' -and \
+              -type f -and \
+              -not -executable \
+              -print \
+            \)
+        )"
+        exit $EXIT_STATUS
+
   config:check:
     desc: Lint and check formatting of configuration files
     cmds: