bug: fix Set-Cookie headers incorrectly concatenated with comma separator

Issue is that commas are valid separators in certain headers (Cookie, Set-Cookie,...).
Switch to semi-colon separated instead -> this only governs the formatted list that appears in the sentry dashboard so is relatively minor.

review comment - #4919 (comment)

./gradlew :sentry-okhttp:test --tests="*SentryOkHttpInterceptorTest.toMap handles duplicate headers correctly*"

Author: 43jay

sentry-okhttp/src/main/java/io/sentry/okhttp/SentryOkHttpInterceptor.kt

@@ -272,8 +272,8 @@ public open class SentryOkHttpInterceptor(
       val value = value(i)
       val existingValue = headers[name]
       if (existingValue != null) {
-        // Concatenate duplicate headers with comma separator
-        headers[name] = "$existingValue, $value"
+        // Concatenate duplicate headers with semicolon separator
+        headers[name] = "$existingValue; $value"
       } else {
         headers[name] = value
       }

sentry-okhttp/src/test/java/io/sentry/okhttp/SentryOkHttpInterceptorTest.kt

@@ -710,9 +710,9 @@ class SentryOkHttpInterceptorTest {
     val interceptor = SentryOkHttpInterceptor(fixture.scopes)
     val headerMap = with(interceptor) { headers.toMap() }
 
-    // Duplicate headers will be collapsed into 1 concatenated entry with ", " separator
-    assertEquals("sessionId=123, userId=456, theme=dark", headerMap["Set-Cookie"])
-    assertEquals("text/html, application/json", headerMap["Accept"])
+    // Duplicate headers will be collapsed into 1 concatenated entry with "; " separator
+    assertEquals("sessionId=123; userId=456; theme=dark", headerMap["Set-Cookie"])
+    assertEquals("text/html; application/json", headerMap["Accept"])
     assertEquals("value", headerMap["Single-Header"])
   }
 }