Fingerprint storage error handling

Motivation:
CI failure: https://ci.swift.org/job/swift-PR-source-compat-suite/5701/artifact/swift-source-compat-suite/

```
error: Failed to get source control fingerprint for swift-log remoteSourceControl https://github.com/apple/swift-log.git version 1.4.2 from storage: Error Domain=NSCocoaErrorDomain Code=513 "You don't have permission to save the file "fingerprints" in the folder "security"." UserInfo={NSFilePath=/Users/buildnode/.swiftpm/security/fingerprints, NSUnderlyingError=0x7feaae439370 {Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"}}
error: Error Domain=NSCocoaErrorDomain Code=513 "You don't have permission to save the file "fingerprints" in the folder "security"." UserInfo={NSFilePath=/Users/buildnode/.swiftpm/security/fingerprints, NSUnderlyingError=0x7feaae439370 {Error Domain=NSPOSIXErrorDomain Code=1 "Operation not permitted"}}
```

Modifications:
`FilePackageFingerprintStorage` to emit warning instead of failing if there are file system related issues.

Author: yim-lee

Sources/PackageFingerprint/FilePackageFingerprintStorage.swift

@@ -48,8 +48,12 @@ public struct FilePackageFingerprintStorage: PackageFingerprintStorage {
             }
 
             callback(.success(fingerprints))
-        } catch {
+        } catch let error as PackageFingerprintStorageError {
             callback(.failure(error))
+        } catch {
+            // Error might be due to file system permission issues, which we don't
+            // have control over, so log instead of throw.
+            observabilityScope.emit(warning: "Failed to read fingerprints for \(package): \(error)")
         }
     }
 
@@ -82,8 +86,12 @@ public struct FilePackageFingerprintStorage: PackageFingerprintStorage {
                 try self.saveToDisk(package: package, fingerprints: packageFingerprints)
             }
             callback(.success(()))
-        } catch {
+        } catch let error as PackageFingerprintStorageError {
             callback(.failure(error))
+        } catch {
+            // Error might be due to file system permission issues, which we don't
+            // have control over, so log instead of throw.
+            observabilityScope.emit(warning: "Failed to write fingerprints for \(package): \(error)")
         }
     }