[REG2.066] Issue 13378 - Wrong failure of template value parameter deduction in IFTI

https://issues.dlang.org/show_bug.cgi?id=13378
The regression has introduced by the change https://github.com/D-Programming-Language/dmd/pull/3536/files#diff-0477a1d81a6a920c99362954179c59c8R5319 in the PR #3536. The deduced value argument identity is not guaranteed by `TemplateParameter::matchArg()` so `Expression::implicitCastTo()` always return a copied object. Therefore we should use `equals` method rather than `!=`.