chore: set Go version to 1.26

- update go.mod
- update Go prerequisite in README.md

Assisted-by: Claude (claude-opus-4-6)
Signed-off-by: Klara Necasova <knecasov@redhat.com>

Author: knecasov

README.md

@@ -9,7 +9,7 @@
 
 ## Prerequisites
 
-- Go 1.26.2 or later
+- Go 1.26 or later
 - `openssl` and `curl` available
 - `jq` to parse JSON output (optional)
 - `npx` to run `openapi-format`

go.mod

@@ -1,6 +1,6 @@
 module github.com/fido-device-onboard/go-fdo-server
 
-go 1.26.2
+go 1.26
 
 require (
 	github.com/elnormous/contenttype v1.0.4