Add missing error code for private method

[GuillaumeGomez]

No description provided.

[rust-highfive]

r? @eddyb

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[kennytm]

Tidy failed, trailing whitespace and duplicated error code.

[00:04:02] tidy error: /checkout/src/test/compile-fail/E0623.rs:13: trailing whitespace
[00:04:03] tidy error: /checkout/src/librustc_typeck/diagnostics.rs:4655: trailing whitespace
[00:04:03] tidy error: /checkout/src/librustc_typeck/diagnostics.rs:4672: trailing whitespace
[00:04:03] tidy error: /checkout/src/librustc_typeck/diagnostics.rs:4676: trailing whitespace
[00:04:03] tidy error: /checkout/src/librustc_typeck/diagnostics.rs:4692: trailing whitespace
[00:04:03] tidy error: duplicate error code: 623
[00:04:03] tidy error: /checkout/src/librustc/diagnostics.rs:2028: E0623, // lifetime mismatch where both parameters are anonymous regions
[00:04:03] tidy error: /checkout/src/librustc_typeck/diagnostics.rs:4647: E0623: r##"
[00:04:03] some tidy checks failed

[eddyb]

r=me with fixed tidy

[GuillaumeGomez]

@bors: r=eddyb

[bors]

📌 Commit 08188c3 has been approved by eddyb

[bors]

⌛ Testing commit 08188c3 with merge 2efdec34faa1d8789f0693392d60d045cb1e1beb...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing 2efdec34faa1d8789f0693392d60d045cb1e1beb to master...

[bors]

👀 Test was successful, but fast-forwarding failed: 422 Update is not a fast forward

[kennytm]

@bors retry #43535

[bors]

⌛ Testing commit 08188c3 with merge 70d962bff091ec76bdb557af632c1ab75aff02b5...

[bors]

⌛ Testing commit 08188c3 with merge 415c86b3fb4a08ffffe63fe99b0f6d64ed1b36b3...

[bors]

⌛ Testing commit 08188c3 with merge 3de807a...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing 3de807a to master...