cmd/protoc-gen-go-grpc: use Error() since no formatting is performed

[ash2k]

RELEASE NOTES: None

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.31%. Comparing base (9b7bd34) to head (bc90c62).
Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8378      +/-   ##
==========================================
+ Coverage   82.18%   82.31%   +0.13%     
==========================================
  Files         419      419              
  Lines       42073    42073              
==========================================
+ Hits        34579    34634      +55     
+ Misses       6028     5983      -45     
+ Partials     1466     1456      -10     

see 24 files with indirect coverage changes

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[ash2k]

Panic in tests seem unrelated:

panic: Log in goroutine after Test/WatchErrorsContainNodeID_ChannelCreationFailure has completed: WARNING ads_stream.go:453 [xds] [xds-client 0x4000608000] [xds-channel 0x400003a1e0] [ads-stream 0x40005ec100] Sending ADS request for type "type.googleapis.com/envoy.config.listener.v3.Listener", resources: [], version: "", nonce: "" failed: EOF  (t=+520.757522ms)
	

goroutine 3135 [running]:
testing.(*common).logDepth(0x4000625500, {0x40000cc240, 0x10a}, 0x3)
	/opt/hostedtoolcache/go/1.24.3/x64/src/testing/testing.go:1064 +0x3bc
testing.(*common).log(...)
	/opt/hostedtoolcache/go/1.24.3/x64/src/testing/testing.go:1046
testing.(*common).Log(0x4000625500, {0x4000594720?, 0x400035c9f0?, 0x1?})
	/opt/hostedtoolcache/go/1.24.3/x64/src/testing/testing.go:1087 +0x50
google.golang.org/grpc/internal/grpctest.(*tLogger).log(0x40001a2ac0, 0x1, 0x4000098008?, {0x0, 0x0}, {0x400005c380, 0x2, 0xa88bc0?})
	/home/runner/work/grpc-go/grpc-go/internal/grpctest/tlogger.go:116 +0x360
google.golang.org/grpc/internal/grpctest.(*tLogger).WarningDepth(0x400035ca98?, 0x2?, {0x400005c380?, 0xa44fa0?, 0x2?})
	/home/runner/work/grpc-go/grpc-go/internal/grpctest/tlogger.go:226 +0x3c
google.golang.org/grpc/grpclog.WarningDepth(0x40005845e0?, {0x400005c380?, 0x10?, 0xc9b7c5?})
	/home/runner/work/grpc-go/grpc-go/grpclog/grpclog.go:153 +0x4c
google.golang.org/grpc/grpclog.(*componentData).WarningDepth(0x40000b0010, 0x1, {0x40005845c0, 0x1, 0x5?})
	/home/runner/work/grpc-go/grpc-go/grpclog/component.go:39 +0x12c
google.golang.org/grpc/internal/grpclog.(*PrefixLogger).Warningf(0x4000196c60, {0xcdc5b4?, 0x0?}, {0x400035cc38, 0x5, 0x5})
	/home/runner/work/grpc-go/grpc-go/internal/grpclog/prefix_logger.go:52 +0xd8
google.golang.org/grpc/xds/internal/clients/xdsclient.(*adsStreamImpl).sendMessageLocked(0x40005ec100, {0xdffe08, 0x4000050d90}, {0x1762060, 0x0, 0x0}, {0xcd070f, 0x35}, {0x0, 0x0}, ...)
	/home/runner/work/grpc-go/grpc-go/xds/internal/clients/xdsclient/ads_stream.go:453 +0x458
google.golang.org/grpc/xds/internal/clients/xdsclient.(*adsStreamImpl).sendMessageIfWritePendingLocked(0x40005ec100, {0xdffe08, 0x4000050d90}, {{0xcd070f, 0x35}, {0xca70a6, 0x10}, 0x1, {0xdeba20, 0x1762060}}, ...)
	/home/runner/work/grpc-go/grpc-go/xds/internal/clients/xdsclient/ads_stream.go:405 +0x1f8
google.golang.org/grpc/xds/internal/clients/xdsclient.(*adsStreamImpl).sendNew(0x40005ec100, {0xdffe08, 0x4000050d90}, {{0xcd070f, 0x35}, {0xca70a6, 0x10}, 0x1, {0xdeba20, 0x1762060}})
	/home/runner/work/grpc-go/grpc-go/xds/internal/clients/xdsclient/ads_stream.go:329 +0x17c
google.golang.org/grpc/xds/internal/clients/xdsclient.(*adsStreamImpl).send(0x40005ec100, {0xe03d58, 0x400003a230})
	/home/runner/work/grpc-go/grpc-go/xds/internal/clients/xdsclient/ads_stream.go:292 +0x170
created by google.golang.org/grpc/xds/internal/clients/xdsclient.(*adsStreamImpl).runner in goroutine 3149
	/home/runner/work/grpc-go/grpc-go/xds/internal/clients/xdsclient/ads_stream.go:229 +0xa8
FAIL	google.golang.org/grpc/xds/internal/clients/xdsclient/test	24.530s