support Go 1.26, release v0.9.0

[abhinav]

Bumps the Go toolchain version to 1.26 and releases v0.9.0.

Test fix

e_go1.24.go tested the analyzer against
type genericAlias[T any] = T.
This construct has always been illegal per the Go spec:
a type alias cannot use its own type parameter as its RHS.
Go 1.18–1.25 silently accepted it due to a gap in
type-checker enforcement.
Go 1.26 closes that gap, causing go/types to reject the file,
which in turn caused the analysis test to fail
with "analysis skipped due to errors in package".

There is no valid Go generic alias form that produces
a composite literal of the aliased struct type,
so the scenario cannot be rewritten with an equivalent valid construct.
The non-generic alias code path in enforce.go is already
exercised by testdata/src/a/a.go and testdata/src/c/c.go,
so test coverage is not lost.

[abhinav]

This change is part of the following stack:

• support Go 1.26, release v0.9.0 #64 ◀

_{Change managed by git-spice.}