runtime/trace: fix TestTraceSymbolize when GOMAXPROCS=1
runtime/trace: fix TestTraceSymbolize when GOMAXPROCS=1

CL 92916 added the GOMAXPROCS test in TestTraceSymbolize.

This test only succeeds when the value of GOMAXPROCS changes.

Since the test calls runtime.GOMAXPROCS(1), it will fails
on machines where GOMAXPROCS=1.

This change fixes the test by calling runtime.GOMAXPROCS(oldGoMaxProcs+1).

Fixes #23816.

Change-Id: I1183dbbd7db6077cbd7fa0754032ff32793b2195
Reviewed-on: https://go-review.googlesource.com/93735
Run-TryBot: David du Colombier <ec8ae1e6620d4bab5e0e7aa2a6ae41aad63e3708@gmail.com>
Reviewed-by: Hyang-Ah Hana Kim <d7e82c3c07f92613bcbf9a1e88f6b96c13caa3b0@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

josharian/go,cloudflare/go,Cofyc/go,codestation/go,nawawi/go,akutz/go,nawawi/go,akutz/go,nawawi/go,golang/go,Cofyc/go,akutz/go,josharian/go,josharian/go,CAFxX/go,codestation/go,CAFxX/go,cloudflare/go,codestation/go,codestation/go,nawawi/go,golang/go,nawawi/go,Cofyc/go,cloudflare/go,Cofyc/go,akutz/go,Cofyc/go,golang/go,CAFxX/go,josharian/go,josharian/go,akutz/go,josharian/go,golang/go,akutz/go,CAFxX/go,nawawi/go,cloudflare/go,CAFxX/go,Cofyc/go,josharian/go,codestation/go,Cofyc/go,akutz/go,golang/go,codestation/go,CAFxX/go,CAFxX/go,CAFxX/go,golang/go,nawawi/go,cloudflare/go,golang/go,codestation/go,nawawi/go,Cofyc/go,akutz/go,golang/go,cloudflare/go,cloudflare/go,codestation/go,cloudflare/go,josharian/go