ci, go.mod: bump to go 1.23 (#1094)

* ci, go.mod: bump to go 1.23

Now that go.mod matches our go version, we can stop setting go version
in CI separately.

Signed-off-by: Casey Callendrello <c1@caseyc.net>

* minor: fix lint errors

Bumping golangci-lint to v1.61 introduced some new reasonable checks;
fix the errors they found.

Signed-off-by: Casey Callendrello <c1@caseyc.net>

* ci: bump golangci-lint to v1.61.0

Also, fix some deprecated config directives.

Signed-off-by: Casey Callendrello <c1@caseyc.net>

---------

Signed-off-by: Casey Callendrello <c1@caseyc.net>

.golangci.yml

@@ -40,6 +40,5 @@ linters-settings:
       - prefix(github.com/containernetworking)
 
 run:
-  skip-dirs:
-    - vendor
   timeout: 5m
+  modules-download-mode: vendor