test against a newer tip

We're just a couple of weeks away from the final release, so
double-check that we still work well with tip.

Update x/tools as well, as it has had some minor fixes for Go 1.17.

.github/workflows/test.yml

@@ -31,7 +31,7 @@ jobs:
     steps:
     - name: Install Go
       env:
-        GO_COMMIT: 1419ca7cead4438c8c9f17d8901aeecd9c72f577 # 2021-05-27
+        GO_COMMIT: 3e48c0381fd1beb78e993e940c3b46ca9898ce6d # 2021-07-21
       run: |
         cd $HOME
         mkdir $HOME/gotip

go.mod

@@ -6,5 +6,5 @@ require (
 	github.com/google/go-cmp v0.5.6
 	github.com/rogpeppe/go-internal v1.8.0
 	golang.org/x/mod v0.4.2
-	golang.org/x/tools v0.1.2
+	golang.org/x/tools v0.1.5
 )

go.sum

@@ -29,8 +29,8 @@ golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/text v0.3.3/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
 golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/tools v0.0.0-20191119224855-298f0cb1881e/go.mod h1:b+2E5dAYhXwXZwtnZ6UAqBI28+e2cm9otk0dWdXHAEo=
-golang.org/x/tools v0.1.2 h1:kRBLX7v7Af8W7Gdbbc908OJcdgtK8bOz9Uaj8/F1ACA=
-golang.org/x/tools v0.1.2/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
+golang.org/x/tools v0.1.5 h1:ouewzE6p+/VEB31YYnTbEJdi8pFqKp4P4n85vwo3DHA=
+golang.org/x/tools v0.1.5/go.mod h1:o0xws9oXOQQZyjljx8fwUC0k7L1pTE6eaCbjGeHmOkk=
 golang.org/x/xerrors v0.0.0-20190717185122-a985d3407aa7/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191011141410-1b5146add898/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=