[receiver/kafka] Fix bug that was blocking shutdown (#32720)

**Description:** <Describe what has changed.>
<!--Ex. Fixing a bug - Describe the bug and how this fixes the issue.
Ex. Adding a feature - Explain what this achieves.-->
The kafka receiver's shutdown method is to cancel the context of a
running sub goroutine. However, a small bug was causing a fatal error to
be reported during shutdown when this expected condition was hit. The
fatal error being reported during shutdown was causing another bug to be
hit,
open-telemetry/opentelemetry-collector#9824.

This fix means that shutdown won't be blocked in expected shutdown
conditions, but the `core` bug referenced above means shutdown will
still be block in unexpected error situations.

This fix is being taken from a comment made by @Dennis8274 on the issue.

**Link to tracking Issue:** <Issue number if applicable>
Fixes #30789

**Testing:** <Describe what testing was performed and which tests were
added.>
Stepped through `TestTracesReceiverStart` in a debugger before the
change to see the fatal status being reported. It was no longer reported
after applying the fix. Manually tested running the collector with a
kafka receiver and saw that before the fix it was indeed being blocked
on a normal shutdown, but after the fix it shutdown as expected.

.chloggen/kafkarec_fix_blocking_shutdown.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: kafkareceiver
+
+# A brief description of the change.  Surround your text with quotes ("") if it needs to start with a backtick (`).
+note: Fix bug that was blocking shutdown
+
+# Mandatory: One or more tracking issues related to the change. You can use the PR number here if no issue exists.
+issues: [30789]
+
+# (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: []

receiver/kafkareceiver/kafka_receiver.go

@@ -5,6 +5,7 @@ package kafkareceiver // import "github.com/open-telemetry/opentelemetry-collect
 
 import (
 	"context"
+	"errors"
 	"fmt"
 	"strconv"
 	"sync"
@@ -160,7 +161,7 @@ func (c *kafkaTracesConsumer) Start(_ context.Context, _ component.Host) error {
 		}
 	}
 	go func() {
-		if err := c.consumeLoop(ctx, consumerGroup); err != nil {
+		if err := c.consumeLoop(ctx, consumerGroup); !errors.Is(err, context.Canceled) {
 			c.settings.ReportStatus(component.NewFatalErrorEvent(err))
 		}
 	}()