Spring boot starter fails to load when an `OpenTelemetry` Bean is supplied

[zeitlinger]

Describe the bug

The OtelMapConverter converter is missing if OTEL_EXPORTER_OTLP_HEADERS=a=b,c=d is supplied.

Steps to reproduce

Index: instrumentation/spring/spring-boot-autoconfigure/src/test/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/properties/SpringConfigPropertiesTest.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
diff --git a/instrumentation/spring/spring-boot-autoconfigure/src/test/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/properties/SpringConfigPropertiesTest.java b/instrumentation/spring/spring-boot-autoconfigure/src/test/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/properties/SpringConfigPropertiesTest.java
--- a/instrumentation/spring/spring-boot-autoconfigure/src/test/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/properties/SpringConfigPropertiesTest.java	(revision 6a47524c808e86bcc58cdc51daa06e440369642d)
+++ b/instrumentation/spring/spring-boot-autoconfigure/src/test/java/io/opentelemetry/instrumentation/spring/autoconfigure/internal/properties/SpringConfigPropertiesTest.java	(date 1748865374032)
@@ -8,6 +8,7 @@
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.entry;
 
+import io.opentelemetry.api.OpenTelemetry;
 import io.opentelemetry.instrumentation.spring.autoconfigure.OpenTelemetryAutoConfiguration;
 import io.opentelemetry.sdk.autoconfigure.spi.ConfigProperties;
 import io.opentelemetry.sdk.autoconfigure.spi.internal.DefaultConfigProperties;
@@ -71,6 +72,7 @@
   void mapFlatHeaders(String key) {
     this.contextRunner
         .withSystemProperties(key + "=a=1,b=2")
+        .withBean(OpenTelemetry.class, OpenTelemetry::noop)
         .run(
             context ->
                 assertThat(getConfig(context).getMap(key))

Expected behavior

Test should not fail

Actual behavior

Test fails

Javaagent or library instrumentation version

2.16.0

Environment

No response

Additional context

No response