fix(actions): keep folded block scalars intact across serialization (#39787) (#39817)

Backport https://github.com/go-gitea/gitea/pull/39787 by @lunny,
including the go-yaml bump. The runner counterpart is
https://gitea.com/gitea/runner/pulls/1321.

Folded (`>`) scalars in workflows gained blank lines and had spaces
turned into newlines every time Gitea re-serialized a job.

- go-yaml main fixes the accumulating blank lines
(https://github.com/yaml/go-yaml/pull/366) and the block scalar
indentation indicators (https://github.com/yaml/go-yaml/pull/414), so
`BlockSafeString` goes away
- The job encoder no longer wraps lines, because go-yaml still wraps
more-indented lines of folded scalars and turns a space into a newline

Fixes https://github.com/go-gitea/gitea/issues/39775

go.sum

@@ -672,8 +672,8 @@ go.yaml.in/yaml/v2 v2.4.4 h1:tuyd0P+2Ont/d6e2rl3be67goVK4R6deVxCUX5vyPaQ=
 go.yaml.in/yaml/v2 v2.4.4/go.mod h1:gMZqIpDtDqOfM0uNfy0SkpRhvUryYH0Z6wdMYcacYXQ=
 go.yaml.in/yaml/v3 v3.0.5 h1:N6y/pJk8buWs9NY5ERU2HSMfm+IuD/OtfdAnq6kESPw=
 go.yaml.in/yaml/v3 v3.0.5/go.mod h1:HVTZu1O7/Vkt2N+BFy8Zza+lnLsABggaTM2ZpNIGuKg=
-go.yaml.in/yaml/v4 v4.0.0-rc.6 h1:1h7H1ohdUh93/FyE4YaDa1Zh64K6VVbjF4K6WUxMtH4=
-go.yaml.in/yaml/v4 v4.0.0-rc.6/go.mod h1:aZqd9kCMsGL7AuUv/m/PvWLdg5sjJsZ4oHDEnfPPfY0=
+go.yaml.in/yaml/v4 v4.0.0-rc.6.0.20261013184558-04dd63131525 h1:FtzHH3s777Nx50YcPAcodAPm1mNakc228nMYbr3f+90=
+go.yaml.in/yaml/v4 v4.0.0-rc.6.0.20261013184558-04dd63131525/go.mod h1:aZqd9kCMsGL7AuUv/m/PvWLdg5sjJsZ4oHDEnfPPfY0=
 go4.org v0.0.0-20260112195520-a5071408f32f h1:ziUVAjmTPwQMBmYR1tbdRFJPtTcQUI12fH9QQjfb0Sw=
 go4.org v0.0.0-20260112195520-a5071408f32f/go.mod h1:ZRJnO5ZI4zAwMFp+dS1+V6J6MSyAowhRqAE+DPa1Xp0=
 golang.org/x/crypto v0.0.0-20190308221718-c2843e01d9a2/go.mod h1:djNgcEr1/C05ACkg1iLfiJU5Ep61QUkGW8qpdssI0+w=