fix(install): Fix parsing error when installing multiple apps w/ specific version

[qwertyhjklxyz]

Description

When foreach returns only one value, the type of $specific_versions_paths is string.
When the value of $specific_versions_paths is a string, the value on the right side of the operator is appended to the string.

Motivation and Context

Closes #6038

How Has This Been Tested?

Before:

$scoop  install [email protected] firefox
...
Couldn't find manifest for 'mysql-workbench.jsonfirefox'.

After:

$scoop  install [email protected] firefox
...
Succeed!

Checklist:

• I have read the Contributing Guide.
• I have ensured that I am targeting the develop branch.
• I have updated the documentation accordingly.
• I have updated the tests accordingly.
• I have added an entry in the CHANGELOG.

[niheaven]

Please test with the new commit.

[qwertyhjklxyz]

Tested and works fine.