go.mod: bump golang to 1.21 (#3158)

Signed-off-by: Steve Kuznetsov <[email protected]>
Upstream-repository: operator-lifecycle-manager
Upstream-commit: f9d8b1e957fa65417ae2682a4d87fdacb61a3b8e

Author: stevekuznetsov

staging/operator-lifecycle-manager/go.mod

@@ -1,6 +1,6 @@
 module github.com/operator-framework/operator-lifecycle-manager
 
-go 1.20
+go 1.21
 
 require (
 	github.com/blang/semver/v4 v4.0.0