test: fix spelling of `caught be the compiler` to `caught by the compiler`

Change-Id: Id21cdce35963dcdb96cc06252170590224c5aa17
GitHub-Last-Rev: 429dad0ceba123415af308179d0d2aa9773e6323
GitHub-Pull-Request: golang/go#28000
Reviewed-on: https://go-review.googlesource.com/c/139424Reviewed-by: Ian Lance Taylor <iant@golang.org>

test/typeswitch2.go

@@ -4,7 +4,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Verify that various erroneous type switches are caught be the compiler.
+// Verify that various erroneous type switches are caught by the compiler.
 // Does not compile.
 
 package main

test/typeswitch3.go

@@ -4,7 +4,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// Verify that erroneous type switches are caught be the compiler.
+// Verify that erroneous type switches are caught by the compiler.
 // Issue 2700, among other things.
 // Does not compile.