Rollup merge of #148175 - osamakader:fix-typos-duplicate-words, r=lcnr

Fix typos: duplicate words in comments

- Fix 'the the' → 'the' in rustc_const_eval
- Fix 'wether' → 'whether' in compiletest
- Fix 'is is' → 'is' in rustc_ast_pretty (2 instances)

Author: Zalathar