format: reformat code with go 1.17

There was a change in how build tags are formatted. Use this as new
reference.

Link: https://go.dev/doc/go1.17#gofmt
Signed-off-by: Robin Jarry <robin@jarry.cc>

lib/keepalive_dummy.go

@@ -1,4 +1,5 @@
-//+build !linux
+//go:build !linux
+// +build !linux
 
 package lib
 

lib/keepalive_linux.go

@@ -1,4 +1,5 @@
-//+build linux
+//go:build linux
+// +build linux
 
 package lib
 

worker/handler_notmuch.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package worker
 

worker/notmuch/eventhandlers.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package notmuch
 

worker/notmuch/events.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package notmuch
 

worker/notmuch/lib/database.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package lib
 

worker/notmuch/lib/thread.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package lib
 

worker/notmuch/message.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package notmuch
 

worker/notmuch/worker.go

@@ -1,4 +1,5 @@
-//+build notmuch
+//go:build notmuch
+// +build notmuch
 
 package notmuch