Update CF gradle plugin to 0.6.46

[wmdietl]

No description provided.

[wmdietl]

I do not understand why I need to use the currently-built artifacts... it used to work before this update.
However #967 fails and I can locally reproduce the failure.
The Out.txt file contains many errors like the following:

Note: Checker Framework 3.42.0-eisop4
error: SourceChecker.typeProcess: unexpected Throwable (NoSuchFieldError) while processing /home/wdietl/workspaces-server/eisop-cf/checker-framework/docs/examples/errorprone/src/main/java/com/example/Demo.java; message: Class org.checkerframework.framework.qual.TypeUseLocation does not have member field 'org.checkerframework.framework.qual.TypeUseLocation TYPE_VARIABLE_USE'
  ; The Checker Framework crashed.  Please report the crash.  Version: Checker Framework 3.42.0-eisop4.
  Checker: class org.checkerframework.checker.nullness.KeyForSubchecker
  Visitor: class org.checkerframework.common.basetype.BaseTypeVisitor
  Compilation unit: /home/wdietl/workspaces-server/eisop-cf/checker-framework/docs/examples/errorprone/src/main/java/com/example/Demo.java
  Last visited tree at line 5 column 1:
  public class Demo {
  Exception: java.lang.NoSuchFieldError: Class org.checkerframework.framework.qual.TypeUseLocation does not have member field 'org.checkerframework.framework.qual.TypeUseLocation TYPE_VARIABLE_USE'; java.lang.NoSuchFieldError: Class org.checkerframework.framework.qual.TypeUseLocation does not have member field 'org.checkerframework.framework.qual.TypeUseLocation TYPE_VARIABLE_USE'
        at org.checkerframework.framework.util.defaults.QualifierDefaults.applyDefaultsElement(QualifierDefaults.java:858)
        at org.checkerframework.framework.util.defaults.QualifierDefaults.applyDefaults(QualifierDefaults.java:597)
        at org.checkerframework.framework.util.defaults.QualifierDefaults.annotate(QualifierDefaults.java:485)
        at org.checkerframework.framework.type.GenericAnnotatedTypeFactory.addComputedTypeAnnotations(GenericAnnotatedTypeFactory.java:2097)
        at org.checkerframework.framework.type.AnnotatedTypeFactory.getAnnotatedType(AnnotatedTypeFactory.java:1502)
        at org.checkerframework.framework.flow.CFAbstractTransfer.getValueFromFactory(CFAbstractTransfer.java:215)
        at org.checkerframework.framework.flow.CFAbstractTransfer.visitNode(CFAbstractTransfer.java:562)
        at org.checkerframework.framework.flow.CFAbstractTransfer.visitNode(CFAbstractTransfer.java:97)
        at org.checkerframework.dataflow.cfg.node.AbstractNodeVisitor.visitMethodAccess(AbstractNodeVisitor.java:240)

The NoSuchFieldError could mean that the wrong checker-qual is used?
Maybe something about how the CF gradle plugin is used should be changed?

This PR allows us to upgrade and I'll turn this comment into a new issue to investigate further.