Fix strict checking for SQLite3 memory filename

[paulbalandan]

Description
According to the SQLite documentation,

Note that in order for the special ":memory:" name to apply and to create a pure in-memory database, there must be no additional text in the filename. Thus, a disk-based database can be created in a file by prepending a pathname, like this: "./:memory:".

Thus, we need to be strictly checking if the name is :memory: rather than checking if it is part of the name.

Checklist:

• Securely signed commits
• Component(s) with PHPdocs
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide