lib: fix MIME overmatch in data URLs
This commit adds the delimiters ^ and $ to the regex that matches the MIME types for "data:URLs". Fixes: https://github.com/nodejs/node/issues/48957
I also added a new test case that expects an ERR_UNKNOWN_MODULE_FORMAT
message for MIME types like this: data:WRONGtext/javascriptFORMAT
.
This is my first time contributing to node. Let me know if I did everything right