Update fetch_sims function for stability (M1 improve support)

[leverdeterre]

Actually, in some cases (for example if you use an M1 processor) Some outputs of the command are missing with the formated JSON. The idea, here is to redirect stderr to nothing to have a valid JSON.

How to reproduce :

• On Bitrise I got this issue when using a M1 Medium Stack and I finally I fix this just by moving to an Intel Medium Stack.
• The problem was blocking the validation process of compiled Pod (because the Pod

pod repo push xxx-build-private-pods XXX-Firebase-ios.podspec --allow-warnings --verbose

Original issue : -> Pod installation complete! There is 1 dependency from the Podfile and 11 total pods installed. Building withxcodebuild`. -> Build-Plugin-Firebase-ios (1.0.3)

• ERROR | [iOS] unknown: Encountered an unknown error (unexpected token at 'objc[5067]: Class AMSupportURLConnectionDelegate is implemented in both /usr/lib/libamsupport.dylib (0x1fbabb838) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa82c8). One of the two will be used. Which one is undefined. objc[5067]: Class AMSupportURLSession is implemented in both /usr/lib/libamsupport.dylib (0x1fbabb888) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa8318). One of the two will be used. Which one is undefined. objc[5067]: Class AppleTypeCRetimerRestoreInfoHelper is implemented in both /usr/lib/libauthinstall.dylib (0x1fbabb650) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa8598). One of the two will be used. Which one is undefined. objc[5067]: Class AppleTypeCRetimerFirmwareAggregateRequestCreator is implemented in both /usr/lib/libauthinstall.dylib (0x1fbabb6a0) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa85e8). One of the two will be used. Which one is undefined. objc[5067]: Class AppleTypeCRetimerFirmwareRequestCreator is implemented in both /usr/lib/libauthinstall.dylib (0x1fbabb6f0) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa8638). One of the two will be used. Which one is undefined. objc[5067]: Class ATCRTRestoreInfoFTABFile is implemented in both /usr/lib/libauthinstall.dylib (0x1fbabb740) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa8688). One of the two will be used. Which one is undefined. objc[5067]: Class AppleTypeCRetimerFirmwareCopier is implemented in both /usr/lib/libauthinstall.dylib (0x1fbabb790) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa86d8). One of the two will be used. Which one is undefined. objc[5067]: Class ATCRTRestoreInfoFTABSubfile is implemented in both /usr/lib/libauthinstall.dylib (0x1fbabb7e0) and /Library/Apple/System/Library/PrivateFrameworks/MobileDevice.framework/Versions/A/MobileDevice (0x106aa8728). One of the two will be used. Which one is undefined. ' /Users/vagrant/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/json-2.6.3/lib/json/common.rb:216:in parse' /Users/vagrant/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/json-2.6.3/lib/json/common.rb:216:inparse' /Users/vagrant/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/fourflusher-2.3.1/lib/fourflusher/find.rb:125:in fetch_sims' /Users/vagrant/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/fourflusher-2.3.1/lib/fourflusher/find.rb:101:inusable_simulators' /Users/vagrant/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/fourflusher-2.3.1/lib/fourflusher/find.rb:97:in simulator' /Users/vagrant/.rbenv/versions/2.7.6/lib/ruby/gems/2.7.0/gems/fourflusher-2.3.1/lib/fourflusher/xcodebuild.rb:7:indestination' / `