fix: prevent CI / build-image failures caused by opencensus

[shvbsle]

CI/build-image failed with the following error:

https fetch: Get "https://go.opencensus.io/?go-get=1": tls: failed to verify certificate: x509: certificate has expired or is not yet valid

Fix:
Setting GOPROXY='https://proxy.golang.org,direct' helps avoid this issue.

Implemented the fix as described in this issue

More about the used proxy:
https://sum.golang.org/

proxy.golang.org - a module mirror which implements the module proxy protocol. For users downloading large numbers of modules (e.g. for bulk static analysis), the mirror supports a separate endpoint /cached-only that instructs the proxy to return only cached content. This will avoid slow downloads, at the cost of possibly missing some rarely-used modules.