Update Go SDK minimum Go version to 1.19

[lostluck]

New dependencies have required the Go SDK minimum Go version to be increased to 1.19 at minimum, which is the current trailing stable Go version.

Users are likely already on 1.20 by now, so this largely affects Beam infra, which has also been updated in this PR.

Motivated by coverage failing when run under Go 1.18: https://github.com/apache/beam/actions/runs/4207200414/jobs/7301693353

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[lostluck]

R: @damccorm

[codecov]

Codecov Report

Merging #25545 (66f0577) into master (20c8d3a) will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #25545      +/-   ##
==========================================
- Coverage   72.80%   72.66%   -0.15%     
==========================================
  Files         750      758       +8     
  Lines       99314   100681    +1367     
==========================================
+ Hits        72304    73155     +851     
- Misses      25648    26118     +470     
- Partials     1362     1408      +46     

Flag	Coverage Δ
go	52.13% <ø> (+0.46%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
sdks/go/pkg/beam/io/mongodbio/read.go	9.03% <0.00%> (-21.94%)	⬇️
sdks/go/pkg/beam/io/mongodbio/coder.go	83.33% <0.00%> (-16.67%)	⬇️
sdks/go/pkg/beam/core/runtime/exec/sdf.go	66.12% <0.00%> (-3.00%)	⬇️
...eam/runners/portability/fn_api_runner/execution.py	92.49% <0.00%> (-0.64%)	⬇️
...ython/apache_beam/io/gcp/bigquery_read_internal.py	57.21% <0.00%> (-0.49%)	⬇️
sdks/python/apache_beam/transforms/combiners.py	93.05% <0.00%> (-0.39%)	⬇️
sdks/python/apache_beam/io/gcp/bigquery.py	71.11% <0.00%> (-0.24%)	⬇️
...ks/python/apache_beam/runners/worker/sdk_worker.py	89.30% <0.00%> (-0.16%)	⬇️
...hon/apache_beam/runners/worker/bundle_processor.py	94.33% <0.00%> (-0.12%)	⬇️
sdks/go/pkg/beam/io/mongodbio/common.go	0.00% <0.00%> (ø)
... and 23 more

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[lostluck]

Given the breadth of effect, I'm going to wait for the various test runs to complete first.

[lostluck]

The last change everything but the go tests passed, and the last change only affected the Go tests.

This should be safe to merge, but I'll keep an eye on the postcommit runs just in case, so we can roll it back promptly.