pgsql: Fix a few typos in JIT comments and README

Fix a few typos in JIT comments and README

Reviewed-by: Abhijit Menon-Sen
Reviewed-by: Andres Freund
Discussion: https://postgr.es/m/CAApHDvobgmCs6CohqhKTUf7D8vffoZXQTCBTERo9gbOeZmvLTw%40mail.gmail.com
Backpatch-through: 11, where JIT was added

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/3248633579e9ed1c718afa70bb93d499fe85d40c

Modified Files
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src/backend/jit/README         | 14 +++++++-------
src/include/jit/llvmjit_emit.h |  2 +-
2 files changed, 8 insertions(+), 8 deletions(-)