Fix regular expressions in workflows (#103)

* Escape `[]` and `()` completely

* Avoid unnecessary escapes

* Tolerate tab for whitespace

* Tolerate other list markers

* Tolerate form-feed for whitespace in task lists

Author: sinsukehlab

.github/workflows/1-add-headers.yml

@@ -59,7 +59,7 @@ jobs:
         uses: skills/action-check-file@v1
         with:
           file: "index.md"
-          search: "# [a-zA-Z0-9]"
+          search: "(?<!#)#{1,6}([\ \\t](.*))?$"
 
       # In README.md, switch step 1 for step 2.
       - name: Update to step 2

.github/workflows/2-add-an-image.yml

@@ -59,7 +59,7 @@ jobs:
         uses: skills/action-check-file@v1
         with:
           file: "index.md"
-          search: "\\!\\[.*](.*)"
+          search: "\\!\\[.*\\]\\(.*\\)"
 
       # In README.md, switch step 2 for step 3.
       - name: Update to step 3

.github/workflows/3-add-a-code-example.yml

@@ -59,7 +59,7 @@ jobs:
         uses: skills/action-check-file@v1
         with:
           file: "index.md"
-          search: "\\`\\`\\`"
+          search: "```"
 
       # In README.md, switch step 3 for step 4.
       - name: Update to step 4

.github/workflows/4-make-a-task-list.yml

@@ -59,7 +59,7 @@ jobs:
         uses: skills/action-check-file@v1
         with:
           file: "index.md"
-          search: "\\- \\[ ] "
+          search: "([\\-\\+\\*]|[0-9]+\\.)[\ \\t]+\\[[\ \\t\\fxX]\\][\ \\t\\f]+\\S.*$"
 
       # In README.md, switch step 4 for step 5.
       - name: Update to step 5