Ignore nullability plugin for 7.0.x

Since later versions of the nullability plugin require JDK 25,
this commit ignores the dependency on 7.0.x, which builds on
JDK 17

Closes gh-18831

Signed-off-by: Josh Cummings <3627351+jzheaux@users.noreply.github.com>

.github/dependabot.yml

@@ -64,6 +64,7 @@ updates:
       - shibboleth
     ignore:
       - dependency-name: com.nimbusds:nimbus-jose-jwt
+      - dependency-name: io.spring.nullability:*
       - dependency-name: org.python:jython
       - dependency-name: org.apache.directory.server:*
       - dependency-name: org.apache.directory.shared:*