Pin circleci/android:api-29-node docker image to previous version with node 12

[ceyhun]

CircleCI circleci/android:api-29-node docker image was recently updated to use node 14
CircleCI-Archived/circleci-dockerfiles@f249389
which started breaking our builds:
https://app.circleci.com/pipelines/github/wordpress-mobile/gutenberg-mobile/8896/workflows/acdfc2fe-3922-40fa-8a35-d15c1c15b4ca/jobs/47353

Full error when node 14 is used

Tried to download(404): https://axonodegit.s3.amazonaws.com/nodegit/nodegit/nodegit-v0.26.2-node-v83-linux-x64.tar.gz 
node-pre-gyp WARN Pre-built binaries not found for [email protected] and [email protected] (node-v83 ABI, glibc) (falling back to source compile with node-gyp)
/bin/sh: 1: krb5-config: not found
gyp: Call to 'krb5-config gssapi --libs' returned exit status 127 while in binding.gyp. while trying to load binding.gyp
gyp
ERR! configure error
gyp
ERR! stack Error: `gyp` failed with exit code: 1
gyp ERR! stack     at ChildProcess.onCpExit (/usr/local/lib/node_modules/npm/node_modules/node-gyp/lib/configure.js:351:16)
gyp ERR! stack     at ChildProcess.emit (events.js:315:20)
gyp ERR!
stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:277:12)
gyp ERR! System Linux 4.15.0-1077-aws
gyp ERR! command "/usr/local/bin/node" "/usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js" "configure" "--fallback-to-build" "--module=/home/circleci/project/gutenberg/node_modules/nodegit/build/Release/nodegit.node" "--module_name=nodegit" "--module_path=/home/circleci/project/gutenberg/node_modules/nodegit/build/Release" "--napi_version=7" "--node_abi_napi=napi" "--napi_build_version=0" "--node_napi_label=node-v83"
gyp ERR! cwd /home/circleci/project/gutenberg/node_modules/nodegit
gyp ERR! node -v v14.15.0
gyp
ERR! node-gyp -v v5.1.0
gyp ERR! not ok
node-pre-gyp
ERR! build error
node-pre-gyp
ERR! stack Error: Failed to execute '/usr/local/bin/node /usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js configure --fallback-to-build --module=/home/circleci/project/gutenberg/node_modules/nodegit/build/Release/nodegit.node --module_name=nodegit --module_path=/home/circleci/project/gutenberg/node_modules/nodegit/build/Release --napi_version=7 --node_abi_napi=napi --napi_build_version=0 --node_napi_label=node-v83' (1)
node-pre-gyp ERR! stack     at ChildProcess.<anonymous> (/home/circleci/project/gutenberg/node_modules/node-pre-gyp/lib/util/compile.js:83:29)
node-pre-gyp ERR! stack     at ChildProcess.emit (events.js:315:20)
node-pre-gyp ERR! stack     at maybeClose (internal/child_process.js:1048:16)
node-pre-gyp
ERR! stack     at Process.ChildProcess._handle.onexit (internal/child_process.js:288:5)
node-pre-gyp
ERR! System Linux 4.15.0-1077-aws
node-pre-gyp ERR! command "/usr/local/bin/node" "/home/circleci/project/gutenberg/node_modules/.bin/node-pre-gyp" "install" "--fallback-to-build"
node-pre-gyp ERR!
cwd /home/circleci/project/gutenberg/node_modules/nodegit
node-pre-gyp ERR! node -v v14.15.0
node-pre-gyp ERR! node-pre-gyp -v v0.13.0
node-pre-gyp ERR! not ok
Failed to execute '/usr/local/bin/node /usr/local/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js configure --fallback-to-build --module=/home/circleci/project/gutenberg/node_modules/nodegit/build/Release/nodegit.node --module_name=nodegit --module_path=/home/circleci/project/gutenberg/node_modules/nodegit/build/Release --napi_version=7 --node_abi_napi=napi --napi_build_version=0 --node_napi_label=node-v83' (1)
[nodegit] ERROR - Could not finish install
[nodegit] ERROR - finished with error code: 1

Pinned the docker image to the previous version using node 12 until we can resolve the issues with node 14.

To test: Check if CI is green

PR submission checklist:

• I have considered adding unit tests where possible.
• I have considered if this change warrants user-facing release notes more info and have added them to RELEASE-NOTES.txt if necessary.

[cameronvoell]

Thanks for figuring this out Ceyhun, looks great