chore: prom translation fix metric comparison func (open-telemetry#35763)

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Ex. Adding a feature - Explain what this achieves.-->
#### Description

<!-- Issue number (e.g. #1234) or full URL to issue, if applicable. -->
#### Link to tracking issue open-telemetry#35741
Fixes 
Wrong comparison func implement in translator/prometheusremotewrite.

<!--Describe what testing was performed and which tests were added.-->
#### Testing

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#### Documentation

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Signed-off-by: Juraj Michalek <[email protected]>

Author: jmichalek132

.chloggen/jm-prom-translation-fix-comparison-func.yaml

@@ -0,0 +1,27 @@
+# Use this changelog template to create an entry for release notes.
+
+# One of 'breaking', 'deprecation', 'new_component', 'enhancement', 'bug_fix'
+change_type: bug_fix
+
+# The name of the component, or a single word describing the area of concern, (e.g. filelogreceiver)
+component: pkg/translator/prometheusremotewrite
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix metric comparison func in prom translation layer
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [35741]
+
+# (Optional) One or more lines of additional information to render under the primary note.
+# These lines will be padded with 2 spaces and then inserted directly into the document.
+# Use pipe (|) for multiline entries.
+subtext:
+
+# If your change doesn't affect end users or the exported elements of any package,
+# you should instead start your pull request title with [chore] or use the "Skip Changelog" label.
+# Optional: The change log or logs in which this entry should be included.
+# e.g. '[user]' or '[user, api]'
+# Include 'user' if the change is relevant to end users.
+# Include 'api' if there is a change to a library API.
+# Default: '[user]'
+change_logs: [user]

pkg/translator/prometheusremotewrite/metrics_to_prw.go

@@ -155,7 +155,7 @@ func isSameMetric(ts *prompb.TimeSeries, lbls []prompb.Label) bool {
 		return false
 	}
 	for i, l := range ts.Labels {
-		if l.Name != ts.Labels[i].Name || l.Value != ts.Labels[i].Value {
+		if l.Name != lbls[i].Name || l.Value != lbls[i].Value {
 			return false
 		}
 	}

pkg/translator/prometheusremotewrite/metrics_to_prw_test.go

@@ -8,6 +8,8 @@ import (
 	"testing"
 	"time"
 
+	"github.com/prometheus/prometheus/prompb"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 	"go.opentelemetry.io/collector/pdata/pcommon"
 	"go.opentelemetry.io/collector/pdata/pmetric"
@@ -156,3 +158,46 @@ func generateExemplars(exemplars pmetric.ExemplarSlice, count int, ts pcommon.Ti
 		e.SetTraceID(pcommon.TraceID{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08, 0x09, 0x0a, 0x0b, 0x0c, 0x0d, 0x0e, 0x0f})
 	}
 }
+
+func TestIsSameMetric(t *testing.T) {
+	tests := []struct {
+		name   string
+		labels func() []prompb.Label
+		ts     func() *prompb.TimeSeries
+		same   bool
+	}{
+		{
+			name: "same",
+			same: true,
+			labels: func() []prompb.Label {
+				return getPromLabels(label11, value11, label12, value12)
+			},
+			ts: func() *prompb.TimeSeries {
+				return getTimeSeries(
+					getPromLabels(label11, value11, label12, value12),
+					getSample(float64(intVal1), msTime1),
+				)
+			},
+		},
+		{
+			name: "not_same",
+			same: false,
+			labels: func() []prompb.Label {
+				return getPromLabels(label11, value11, label12, value12)
+			},
+			ts: func() *prompb.TimeSeries {
+				return getTimeSeries(
+					getPromLabels(label11, value11, label21, value21),
+					getSample(float64(intVal1), msTime1),
+				)
+			},
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			same := isSameMetric(tt.ts(), tt.labels())
+			assert.Equal(t, tt.same, same)
+		})
+	}
+}