`-static-msg` raise an error on static string concatenation

[gnuletik]

The following code:

logger.Warn(
    "this is a really long message, that " +
    "requires to split the line",
)

Raises the following error in golangci-lint@v2.0.2 (which uses simpler.org/sloglint@v0.9.0):

message should be a string literal or a constant (sloglint)

The message is constant even though it is built with string concatenation to split long lines.

Related to #17