go: Bump Go to 1.26.3

[peternose]

No description provided.

[netlify]

✅ Deploy Preview for oasisprotocol-oasis-core canceled.

Name	Link
🔨 Latest commit	18756c5
🔍 Latest deploy log	https://app.netlify.com/projects/oasisprotocol-oasis-core/deploys/6a1aa0b3c4363b0008c3fd6c

[codecov]

Codecov Report

❌ Patch coverage is 76.71233% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 63.75%. Comparing base (2df371d) to head (18756c5).

Files with missing lines	Patch %	Lines
go/common/crypto/tls/verify.go	42.85%	1 Missing and 3 partials ⚠️
go/runtime/host/protocol/connection.go	0.00%	3 Missing ⚠️
go/runtime/host/sgx/common/metrics.go	0.00%	3 Missing ⚠️
go/common/grpc/credentials.go	71.42%	1 Missing and 1 partial ⚠️
go/common/grpc/grpc.go	80.00%	1 Missing and 1 partial ⚠️
go/runtime/host/loadbalance/host.go	0.00%	2 Missing ⚠️
go/common/grpc/auth/auth_tls_pubkeys.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6540      +/-   ##
==========================================
- Coverage   64.03%   63.75%   -0.29%     
==========================================
  Files         698      698              
  Lines       68292    68293       +1     
==========================================
- Hits        43734    43542     -192     
- Misses      19605    19757     +152     
- Partials     4953     4994      +41     

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