x/tools/cmd/guru: TestGuru consistently failing since CL 295271

[bcmills]

https://build.golang.org/log/da6da4438e6dd13146dc1090c989f30fc0edf2a1:

testdata/src/softerrs/main.go:8:6: i declared but not used
--- FAIL: TestGuru (0.00s)
    --- FAIL: TestGuru/describe (2.57s)
        guru_test.go:307: Guru tests for testdata/src/describe/main.go failed: exit status 1.
            --- testdata/src/describe/main.golden	2021-02-22 15:35:19.000000000 +0000
            +++ /workdir/tmp/main.got550239221	2021-02-23 04:46:18.741397903 +0000
            @@ -24,7 +24,7 @@
             import of package "unsafe"
             	builtin Alignof 
             	builtin Offsetof
            -	type  Pointer  unsafe.Pointer
            +	type  Pointer  Pointer
             	builtin Sizeof  
             
             -------- @describe type-ref-builtin --------
            
FAIL
FAIL	golang.org/x/tools/cmd/guru	87.042s

From looking at https://build.golang.org/?repo=golang.org%2fx%2ftools, the failure appears to have started at CL 295271 (#44515) in the main repo (@findleyr, @griesemer).

[gopherbot]

Change https://golang.org/cl/296289 mentions this issue: cmd/guru: update golden file (fix test failure)