fix: lower log level for missing base ref detection (EME-369)

Changes the logging level from warn to info when failing to detect base
branch reference in build uploads. This reduces noise in build logs for
common scenarios including detached HEAD states in PRs and main/master
branch builds where base ref detection failures are expected.

Also removes --log-level=error from test to allow info messages to be seen.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: runningcode

src/commands/build/upload.rs

@@ -192,7 +192,7 @@ pub fn execute(matches: &ArgMatches) -> Result<()> {
                             Some(base_ref_name)
                         }
                         Err(e) => {
-                            warn!("Could not detect base branch reference: {}", e);
+                            info!("Could not detect base branch reference: {}", e);
                             None
                         }
                     })

tests/integration/_cases/build/build-upload-ipa.trycmd

@@ -1,5 +1,5 @@
 ```
-$ sentry-cli build upload tests/integration/_fixtures/build/ipa.ipa --head-sha test_head_sha --log-level=error
+$ sentry-cli build upload tests/integration/_fixtures/build/ipa.ipa --head-sha test_head_sha
 ? success
 Successfully uploaded 1 file to Sentry
   - tests/integration/_fixtures/build/ipa.ipa (http[..]/wat-org/preprod/wat-project/some-text-id)