@deprecated annotation needs to be constant

[mkurz]

Otherwise scaladoc will complain in Scala 2.13.6
See scala/scala#9336

Happened to me when I wanted to bump to Scala 2.13.7 in omnidoc:
playframework/omnidoc#186

[error] /home/travis/build/playframework/omnidoc/target/scala-2.13/omnidoc/sources/com.typesafe.play-play-slick_2.13-5.0.0/play/api/db/slick/DatabaseConfigProvider.scala:95:100: annotation argument needs to be a constant; found: scala.Predef.augmentString("Use DatabaseConfigProvider#get[P] or SlickApi#dbConfig[P](\"default\") on injected instances").stripMargin
[error]     "Use DatabaseConfigProvider#get[P] or SlickApi#dbConfig[P](\"default\") on injected instances".stripMargin,
[error]                                                                                                    ^
[warn] one warning found
[error] one error found
[error] (Omnidoc / scaladoc) Scaladoc generation failed

https://app.travis-ci.com/github/playframework/omnidoc/jobs/554426274#L1281

[mkurz]

@Mergifyio backport 5.0.x

[mergify]

backport 5.0.x

🟠 Waiting for conditions to match

• merged [:pushpin: backport requirement]

[mergify]

backport 5.0.x

✅ Backports have been created

• #642 @deprecated annotation needs to be constant (backport #641) has been created for branch 5.0.x

[xuwei-k]

• 😢 remove invalid stripMargin #602

[mkurz]

@xuwei-k Sorry, I didn't see you pull request!