bugfix(at-import-partial-extension): fixer incorrectly replaces filename

[chimurai]

Hi, my first contrib here. 👋

While fixing a large codebase I noticed the at-import-partial-extension fixer incorrectly fixed certain files when they have .scss in their filename. (example: component.scss-theme.scss)

---

currently:
at-import-partial-extension's fixer incorrectly replaced all .scss occurences in a filename.

- @import "component.scss-theme.scss";
+ @import "component-theme";

expected:
at-import-partial-extension's fixer should only replace the .scss extension (not when .scss is used in the filename itself)

- @import "component.scss-theme.scss";
+ @import "component.scss-theme";

[kristerkari]

Thanks @chimurai ! Looks really good!