Fix regular expression anchors

[matt257]

Tracking issue for:

• https://github.com/OSC/ondemand/security/code-scanning/3

opened as a test for opening issues from code scanning alerts

[matt257]

Regular expressions in Ruby can use anchors to match the beginning and end of a string. However, if the ^ and $ anchors are used, the regular expression can match a single line of a multi-line string. This allows bad actors to bypass your regular expression checks and inject malicious input.

Recommendation
Use the \A and \z anchors since these anchors will always match the beginning and end of the string, even if the string contains newlines.