vmalert: fix vmalert_remotewrite_send_duration_seconds_total metric…

[Abirdcfly]

… value

The deferred call's arguments are evaluated immediately, but the function call is not executed until the surrounding function returns.

For a simulation, see: https://go.dev/play/p/XTxYljyk1VZ

package main

import (
	"fmt"
	"time"
)

func main() {
	B()
	A()
}
func A() {
	timeStart := time.Now()
	defer Add(time.Since(timeStart).Seconds())  // 0
	time.Sleep(time.Second)
}

func B() {
	timeStart := time.Now()
	defer func() {
		Add(time.Since(timeStart).Seconds())  // 1
	}()
	time.Sleep(time.Second)
}

func Add(d float64) {
	fmt.Println(d)
}

[Haleygo]

LGTM!
Thanks for the fix!

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: -0.02% ⚠️

Comparison is base (527cfa2) 61.10% compared to head (4c815ed) 61.08%.
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4801      +/-   ##
==========================================
- Coverage   61.10%   61.08%   -0.02%     
==========================================
  Files         381      381              
  Lines       71586    71587       +1     
==========================================
- Hits        43740    43730      -10     
- Misses      25458    25466       +8     
- Partials     2388     2391       +3     

Files Changed	Coverage Δ
app/vmalert/main.go	39.23% <100.00%> (+0.15%)	⬆️
app/vmalert/remotewrite/remotewrite.go	67.72% <100.00%> (+0.34%)	⬆️
app/vmalert/web.qtpl	71.32% <100.00%> (ø)

... and 9 files with indirect coverage changes

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[valyala]

FYI, this pull request has been included in v1.93.0.