chore: Update go declaration to have point version (#1484)

Our understanding is that without the patch version, every run of "go
mod tidy" will write a toolchain directive in the file, which will
result in a diff from contributors with different point versions of go,
which is noisy and prone to breaking CI.

Signed-off-by: Will Murphy <will.murphy@anchore.com>

go.mod

@@ -1,8 +1,6 @@
 module github.com/anchore/grype
 
-go 1.21
-
-toolchain go1.21.0
+go 1.21.1
 
 require (
 	github.com/CycloneDX/cyclonedx-go v0.7.1