Use jwt-go (golang-jwt) instead of deprecated jws (x/oauth2/jws)

golang.org/x/oauth2/jws is deprecated: this package is not intended for public use and
might be removed in the future. It exists for internal use only. Please switch to another
JWS package or copy this package into your own source tree.

github.com/golang-jwt/jwt/v4 seems to be a good alternative, and was already
an implicit dependency.

.golangci.yml

@@ -33,11 +33,6 @@ issues:
       - staticcheck
       text: 'SA1019: "github.com/rclone/rclone/cmd/serve/httplib" is deprecated'
 
-    # TODO: Remove if/when this is fixed by merging PR #6277.
-    - linters:
-      - staticcheck
-      text: 'SA1019: "golang.org/x/oauth2/jws" is deprecated'
-
 run:
   # timeout for analysis, e.g. 30s, 5m, default is 1m
   timeout: 10m