feat: Update grep to use perl-regexp option (#5)

* feat: Update grep to use perl-regexp option

* Update copyright year in README.md

Author: sinsukehlab

README.md

@@ -16,4 +16,4 @@ Example use:
           search: "# [a-zA-Z0-9]"
 ```
 
-© 2023 GitHub • [Code of Conduct](https://www.contributor-covenant.org/version/2/1/code_of_conduct/code_of_conduct.md) • [MIT License](https://gh.io/mit)
+© 2024 GitHub • [Code of Conduct](https://www.contributor-covenant.org/version/2/1/code_of_conduct/code_of_conduct.md) • [MIT License](https://gh.io/mit)

action.yml

@@ -31,7 +31,7 @@ runs:
         # So that its still a single \ in bash
 
         echo "Check that $FILE includes $SEARCH"
-        if grep --extended-regexp "$SEARCH" -- $FILE
+        if grep --perl-regexp "$SEARCH" -- $FILE
         then
           echo "Found $SEARCH in $FILE"
         else