Add test for #10759

The test tries to run `cabal` in an environment where `GHC_ENVIRONMENT`
is set, and checks that the compilation of a simple package isn't
affected by the variable being set.

Author: mpickering

cabal-testsuite/PackageTests/EnvironmentFile/CHANGELOG.md

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+# Revision history for EnvironmentFile
+
+## 0.1.0.0 -- YYYY-mm-dd
+
+* First version. Released on an unsuspecting world.

cabal-testsuite/PackageTests/EnvironmentFile/EnvironmentFile.cabal

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+cabal-version:   3.14
+name:            EnvironmentFile
+version:         0.1.0.0
+license:         NONE
+author:          Matthew Pickering
+maintainer:      [email protected]
+build-type:      Simple
+extra-doc-files: CHANGELOG.md
+
+common warnings
+    ghc-options: -Wall
+
+executable EnvironmentFile
+    import:           warnings
+    main-is:          Main.hs
+    build-depends:    base ^>=4.20.0.0
+    hs-source-dirs:   app
+    default-language: Haskell2010

cabal-testsuite/PackageTests/EnvironmentFile/app/Main.hs

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+module Main where
+
+main :: IO ()
+main = putStrLn "Hello, Haskell!"

cabal-testsuite/PackageTests/EnvironmentFile/cabal.test.hs

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+import Test.Cabal.Prelude
+import System.FilePath
+main = cabalTest $ recordMode DoNotRecord $ do
+    env <- getTestEnv
+    let cur_dir = testCurrentDir env
+    -- Set GHC_ENVIRONMENT to a file which contains garbage
+    withEnv [("GHC_ENVIRONMENT", Just (cur_dir </> "ghc.environment"))] $ do
+        cabal "build" ["all"]

cabal-testsuite/PackageTests/EnvironmentFile/ghc.environment

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+this-file-(ghc.environment)-contains-garbage-it-should-not-be-read