mac build: bump declared min supported macos version (10.13->11)

due to the qt 5.15 -> qt 6.7 bump

related https://github.com/spesmilo/electrum/issues/3685

contrib/osx/README.md

@@ -33,7 +33,7 @@ Notes about compatibility with different macOS versions:
     `notarytool` requires Xcode 13+, and that in turn requires macOS 11.3+.
 
 We currently build the release binaries on macOS 11.7.10, and these seem to run on
-10.14 or newer. (note: 10.13 might also work, haven't tested)
+11 or newer.
 
 
 #### Notes about reproducibility

contrib/osx/osx.spec

@@ -134,7 +134,7 @@ app = BUNDLE(
                 'CFBundleURLName': 'bitcoin',
                 'CFBundleURLSchemes': ['bitcoin', 'lightning', ],
             }],
-        'LSMinimumSystemVersion': '10.13.0',
+        'LSMinimumSystemVersion': '11',
         'NSCameraUsageDescription': 'Electrum would like to access the camera to scan for QR codes',
     },
 )