Don't lint the generated deepcopy file

I found it a bit hard to understand how to configure this but looking at
the example config
(https://github.com/golangci/golangci-lint/blob/master/.golangci.example.yml)
this seems right.

Since we don't control these files, it makes sense to skip linting them.

Recently we bumped the linter, which pulled in a new version of gosec,
which started flagging "Implicit memory aliasing in for loop" in the
generated files. This is a bit weird but at least we know that the
values are being used immediately and not stored, so it seems (famous
last words) unlikely to hit the bug these are trying to catch
(this issue has an example of the kind of bug this catches:
https://github.com/trailofbits/gosec/issues/1)

e.g. the code getting flagged:
```
		for key, val := range *in {
			var outVal *PipelineRunTaskRunStatus
			if val == nil {
				(*out)[key] = nil
			} else {
				in, out := &val, &outVal
				*out = new(PipelineRunTaskRunStatus)
				(*in).DeepCopyInto(*out)
			}
			(*out)[key] = outVal
		}
```

.golangci.yml

@@ -24,6 +24,8 @@ run:
   issues-exit-code: 1
   build-tags:
   - e2e
+  skip-files:
+  - path: .*/zz_generated.deepcopy.go
   skip-dirs:
   - vendor
   - pkg/client